Hybrid aerobic and anaerobic wastewater and sludge treatment systems and methods

ABSTRACT

A hybrid method and system of treating wastewater with reduced energy usage is disclosed. The treatment system has a sorption system, an anaerobic digester that digests or converts at least a portion of the solids or sludge from the sorption system, and an aerobic treatment tank that partially reduces oxygen demand of a portion of the sludge from the sorption tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 as a continuationof U.S. patent application Ser. No. 13/034,269, filed Feb. 24, 2011,titled HYBRID AEROBIC AND ANAEROBIC WASTEWATER AND SLUDGE TREATMENTSYSTEMS AND METHODS which claims priority under 35 U.S.C. §119 of U.S.Provisional Application Ser. No. 61/308,297, filed Feb. 25, 2010, titledRECYCLE METHANOGEN AND NITRIFICATION BACTERIA IN A BIO-SORPTION ANDANAEROBIC DIGESTION PROCESS AND NUTRIENT RECOVERY IN A BIO-SORPTION ANDANAEROBIC DIGESTION PROCESS. This application also claims priority under35 U.S.C. §120 as a continuation-in-part of U.S. patent application Ser.No. 12/934,927, filed Dec. 13, 2010, titled HYBRID AEROBIC AND ANAEROBICWASTEWATER AND SLUDGE TREATMENT SYSTEMS AND METHODS, which is a nationalstage entry under 35 U.S.C. §371 of PCT Application Serial No.PCT/US2009/001949, filed Mar. 27, 2009, titled HYBRID AEROBIC ANDANAEROBIC WASTEWATER AND SLUDGE TREATMENT SYSTEMS AND METHODS whichclaims the benefit of U.S. Provisional Application Ser. No. 61/040,179,filed Mar. 28, 2008, titled GREEN WASTEWATER TREATMENT PROCESS, U.S.Provisional Application Ser. No. 61/041,720, filed Apr. 2, 2008, titledHYBRID PROCESS TO CONVERT ANAEROBIC WASTEWATER TREATMENT TO ANAEROBICSLUDGE TREATMENT, and to U.S. Provisional Application Ser. No.61/046,631, filed Apr. 21, 2008, titled MINIMIZING ENERGY USAGE BYAPPLYING HYBRID ANAEROBIC DIGESTION FOR WATER RECLAMATION. Each of theseapplications is incorporated herein by reference for all purposes.

1. FIELD OF THE INVENTION

The present invention relates to systems and processes of wastewatertreatment and, in particular, to systems and methods of treatingwastewater utilizing biological sorption, aerobic treatment, anaerobicsludge digestion, sequencing batch reactors with membrane filtrationsystems.

2. DESCRIPTION OF THE RELATED ART

Pilgram et al., in U.S. Pat. No. 6,383,389, which is incorporated hereinby reference for all purposes, including but not limited to sequences orstages that can be used in batch or continuous reactors, teach awastewater treatment system and method of controlling the treatmentsystem. A control system can sequence and supervise treatment steps in abatch flow mode of operation or a continuous flow mode.

Sutton, in U.S. Patent Application No. 2008/0223783, teaches awastewater treatment system and a method of treating wastewater. Thesystem includes an aerobic membrane bioreactor and an anaerobic digestersystem connected to receive wasted solids continuously from the aerobicmembrane bioreactor. The system also returns effluent from the anaerobicdigester system continuously to the aerobic membrane bioreactor.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present disclosure, there isprovided a method for treating wastewater. The method comprisesproviding a wastewater to be treated, promoting biological sorption ofthe wastewater to be treated in a biological sorption contact tank toproduce a mixed liquor, producing a solids-rich sludge and a solids-leanportion from the mixed liquor, combining a first portion of thesolids-rich sludge with the wastewater to be treated, introducing asecond portion of the solids-rich sludge into a sludge thickener toproduce a thickened sludge and a sludge-lean stream, combining thesludge-lean stream with the wastewater to be treated, anaerobicallydigesting the thickened sludge to produce an anaerobically digestedsludge, combining a first portion of the anaerobically digested sludgewith the wastewater to be treated, aerobically treating a second portionof the anaerobically digested sludge to form an at least partiallyaerobically treated sludge, and combining the at least partiallyaerobically treated sludge with the wastewater to be treated.

In some embodiments, the method further comprises directing the firstportion of the solids-rich sludge into a stabilization tank prior tocombining the first portion of the solids-rich sludge with thewastewater to be treated.

In some embodiments, the method further comprises directing a greateramount of the solids-rich sludge into the stabilization tank than intothe sludge thickener.

In some embodiments, the method further comprises directing thesludge-lean stream into the stabilization tank prior to combining thesludge-lean stream with the wastewater to be treated.

In some embodiments, the method further comprises directing the firstportion of the anaerobically digested sludge into the stabilization tankprior to combining the first portion of the anaerobically digestedsludge with the wastewater to be treated.

In some embodiments, the method further comprises directing the portionof the at least partially aerobically treated sludge to the biologicalsorption contact tank.

In some embodiments, the method further comprises directing thesludge-lean stream into a stabilization tank prior to combining thesludge-lean stream with the wastewater to be treated.

In some embodiments, the method further comprises directing the firstportion of the anaerobically digested sludge into a stabilization tankprior to combining the first portion of the anaerobically digestedsludge with the wastewater to be treated.

In some embodiments, the method further comprises directing the portionof the at least partially aerobically treated sludge to the biologicalsorption contact tank.

In accordance with an aspect of the present disclosure, there isprovided a method for treating wastewater. The method comprisesproviding a wastewater to be treated, separating the wastewater to betreated into a solids-lean wastewater and a solids-rich wastewater,promoting biological sorption of the solids-lean wastewater in abiological sorption contact tank to produce a mixed liquor, producing asolids-rich sludge and a solids-lean portion from the mixed liquor,combining a first portion of the solids-rich sludge with the wastewaterto be treated, introducing a second portion of the solids-rich sludgeinto a sludge thickener to produce a thickened sludge and a sludge-leanstream, combining the sludge-lean stream with the wastewater to betreated, directing the thickened sludge together with the solids-richwastewater into an anaerobic digester, anaerobically digesting thethickened sludge and the solids-rich wastewater together in theanaerobic digester to produce an anaerobically digested sludge, andcombining a first portion of the anaerobically digested sludge with thewastewater to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Theidentical or nearly identical component or feature that is illustratedin various figures is represented by a like numeral. For purposes ofclarity, not every component may be labeled in every drawing, nor isevery component of each embodiment of the invention shown whereillustration is not necessary to allow those of ordinary skill in theart to understand the invention. In the drawings:

FIG. 1 is a flow diagram illustrating a representative treatment systempertinent to one or more aspects of the invention;

FIG. 2 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 3 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 4 is a graph of energy gain from methane production relative to theamount of activated sludge (percent) entering the anaerobic digester fora treatment system pertinent to one or more aspects of the invention;

FIG. 5 is a graph of aeration energy reduction versus percent activatedsludge entering the anaerobic digester for a treatment system pertinentto one or more aspects of the invention;

FIG. 6 is a graph of net energy gain versus percent activated sludgeentering the anaerobic digester for a treatment system pertinent to oneor more aspects of the invention;

FIG. 7 is a graph of percentage of the COD removal by anaerobic digesterenergy versus percent activated sludge entering the anaerobic digesterfor a treatment system pertinent to one or more aspects of theinvention;

FIG. 8 is a graph of sludge yield versus percent return activated sludgeentering the anaerobic digester for a treatment system pertinent to oneor more aspects of the invention;

FIG. 9 is a process flow diagram illustrating another representativetreatment system pertinent to one or more aspects of the invention.

FIG. 10 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 11 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 12 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 13 is a flow diagram illustrating another representative treatmentsystem pertinent to one or more aspects of the invention;

FIG. 14 is a chart illustrating the concentration of various substancesin a comparative treatment system;

FIG. 15 is a chart illustrating the concentration of various substancesin a representative treatment system;

FIG. 16 is a chart illustrating the concentration of various substancesin another representative treatment;

FIG. 17 is a chart illustrating the concentration of various substancesin a comparative and two representative treatment systems;

FIG. 18 illustrates daily biogas production during a test of tworepresentative test systems and a comparative system;

FIG. 19 illustrates a hypothetical variation in wastewater influent withtime of day at a hypothetical municipal wastewater treatment plant;

FIG. 20 illustrates a percentage of total wastewater influent chemicaloxygen demand removed in an anaerobic digester in a simulation of asystem in accordance with the present invention;

FIG. 21 illustrates a percentage of total wastewater influent chemicaloxygen demand removed in an aerobic digester in a simulation of a systemin accordance with the present invention;

FIG. 22 illustrates specific energy consumption used to treat wastewaterin a simulation of a system in accordance with the present invention;and

FIG. 23 illustrates waste sludge production in a simulation of a systemin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Aspects and embodiments of this invention are directed to systems andmethods of treating water, wastewater, or sludge to, for example, reduceoxygen demand, such as the biological oxygen demand (BOD), and renderthe water suitable for secondary uses or discharge to the environment.One or more aspects of the invention relate to wastewater treatmentsystems and methods of operation and facilitating thereof. Furtheraspects of the invention can pertain to generating, or collecting abyproduct such as an off-gas and utilizing the byproduct as a fuelsource for one or more unit operations of the treatment system. Furtheraspects of the invention can pertain to recovering phosphorous and/ornitrogen containing compounds from wastewater for use as, for example,fertilizer.

The invention is not limited in its application to the details ofconstruction and the arrangement of components, systems, or subsystemsset forth herein, and is capable of being practiced or of being carriedout in various ways. Typically, the water to be treated, such aswastewater or a wastewater stream, contains waste matter which, in somecases, can comprise solids and soluble and insoluble organic andinorganic material. Prior to discharge to the environment, such streamsmay require treatment to decontaminate or at least partially render thewastewater streams benign or at least satisfactory for discharge underestablished regulatory requirements or guidelines. For example, thewater can be treated to reduce its COD, BOD, and/or other characteristicsuch as Giardia content to within acceptable limits.

Some aspects of the invention can involve biologically treatingwastewater by promoting bacterial digestion of biodegradable material ofat least a portion of at least one species in the wastewater. Furtheraspects of the invention can relate to effecting or at leastfacilitating separation of converted, digested biodegraded solidmaterial from the entraining liquid. Still further aspects of theinvention can relate to effecting or at least facilitating reducing anamount of solids from the wastewater or water to be treated.

Some aspects of the invention can involve recovering one or more desiredminerals or compounds, for example, phosphorous and/or nitrogencontaining compounds, from the wastewater.

As used herein, the terms “water,” “wastewater,” and “wastewater stream”can refer to water to be treated such as streams or bodies of water fromresidential, commercial, or municipal, industrial, and agriculturalsources, as well as mixtures thereof, that typically contain at leastone undesirable species, or pollutant, comprised of biodegradable,inorganic or organic, materials which can be decomposed or converted bybiological processes into environmentally benign or at least lessobjectionable compounds. The water to be treated can also containbiological solids, inert materials, organic compounds, includingrecalcitrant or a class of compounds that are difficult to biodegraderelative to other organic compounds as well as constituents fromancillary treatment operations such as, but not limited to nitrosaminesand endocrine disruptors.

A “solids-lean” or “sludge-lean” sludge, portion, stream, or fluid istypically a liquid, such as water that has been at least partiallytreated, having less suspended solids relative to a starting mixedliquor or sludge after one or more settling or separation operations.Conversely, a “solids-rich” or “sludge-rich” sludge, portion, stream, orfluid is typically a liquid, such as water that has been at leastpartially treated, having a higher solids concentration relative to thestarting mixed liquor or sludge after one or more settling or separationoperations. For example, a mixed liquor having suspended solids can beallowed to promote settling of at least a portion of the solidssuspended therein; the resultant water body, as a consequence ofartificially induced or natural gravitational forces will typically havea lower water layer and an upper water layer, wherein the lower layerhas a higher concentration of solids, relative to the starting mixedliquor and to the upper, solids-lean water layer. Further, thesolids-lean water layer will typically have a lower concentration ofsolids suspended therein relative to the starting mixed liquor.Separation operations that can be utilized to effect or promote someaspects of the invention can utilize gravitational forces produce any ofthe solids-rich, solids-lean, sludge-rich, and sludge-lean portions orstreams. Other separation operations can involve filtration.

A “treated” portion is typically water having less undesirable speciesor pollutants relative to a starting “solids-lean” portion after one ormore treatment stages, such as one or more biological or separationoperations. A “solids-lean” portion having undesirable species such assoluble inorganic or organic compounds can be introduced to one or moreseparation operations, such as a membrane filtration device or amembrane bioreactor that may retain the inorganic or organic compoundson a first side of a filter as a “second mixed liquor,” while allowingthe “treated” portion to pass through the filter.

One or more of the inventive systems disclosed herein can comprise oneor more biologically-based or non-biologically-based unit operations.The systems and techniques of the invention can be effected as, or atleast as a portion, of decontamination or treatment systems thattypically include one or more of pre-treatment, primary treatment,secondary treatment, and post-treatment or polishing operations. Thetreatment facilities that can employ one or more aspects of theinvention can include at least one of the pre-treatment, primarytreatment, secondary treatment, and post-treatment or polishingoperations.

Pretreatment systems and operations may remove grit, sand, and gravel.Primary treatment operations or systems can involve at least partialequalization, neutralization, and/or removal of large insoluble materialof the water to be treated such as, but not limited to fats, oils, andgrease. The pretreatment and primary treatment operations may becombined to remove such materials as well as settleable solids andfloating bodies, and insoluble objects such as rags and sticks. Forexample, primary clarifiers may be utilized to separate solids.

Secondary treatment unit operations or systems can involve biologicaltreatment such as those that typically employ a biomass with bacteria ora consortium of microorganisms to at least partially hydrolyze orconvert biodegradable material such as, but not limited to sugar, fat,organic molecules, and compounds that create an oxygen demand in thewater. Indeed, some advantageous aspects of the invention can utilizebiological processes and systems to remove or convert at least a portionof organic material in the water to be treated.

Post-treatment or polishing operations or systems can include biologicaltreatments, chemical treatments, and separation systems. Thepost-treatment operations may include processes that involve biologicalnitrification/denitrification and phosphorus removal. Chemicaltreatments that can be used may include chemical oxidation and chemicalprecipitation. Separation systems can include dissolved inorganic solidsremoval by ion exchange, ultrafiltration, reverse osmosis, orelectrodialysis. Further treatment processes can involve disinfection,decontamination or inactivation of at least a portion of any residualmicroorganisms by chemical or physical means. For example, disinfectioncan be effected by exposure to any one or more of oxidizing agents or toactinic radiation. Commercially available separation systems that may beutilized in some embodiments of the invention include those employingthe CMF-S™ continuous membrane filtration modules as well as the MEMCOR®CMF (Pressurized) XP, CP, and XS membrane filtration systems, fromSiemens Water Technologies Corp. Other separators that can be usedinclude filter presses and centrifuges.

Some embodiments of the treatment systems of the invention can comprisea source of wastewater to be treated, a biological sorption tank havinga sorption tank inlet fluidly connected to the source of the wastewater.The treatment systems of the invention can also comprise a separatorfluidly having a separator inlet fluidly connected downstream from thebiological sorption tank, a sludge outlet, and a solids-lean outlet. Thetreatment systems of the invention can further comprise an aerobictreatment tank having an aerobic tank inlet fluidly connected downstreamfrom the sludge outlet, and an at least partially aerobically treatedsludge outlet fluidly connected to the sorption tank inlet. Thetreatment systems of the invention can additionally comprise ananaerobic digester having a digester inlet fluidly connected downstreamfrom the sludge outlet, and a digested sludge outlet fluidly connectedupstream of the sorption tank inlet.

Non-limiting examples of clarifiers or components thereof that can beutilized in one or more configurations of the present treatment systemsinclude, but are not limited to the ENVIREX® FLOC-CLARIFIER system, theSPIRACONE™ upflow sludge blanket clarifier, RIM-FLO® circular clarifier,and the TRANS-FLO® clarifier, from Siemens Water Technologies Corp.

Membrane bioreactor (MBR) systems that can be utilized in accordancewith one or more configurations disclosed herein include, but are notlimited to, the MEMPULSE™ membrane bioreactor system, the PETRO™membrane bioreactor system, the Immersed Membrane Bioreactor System, andthe XPRESS™ MBR Packaged Wastewater System, from Siemens WaterTechnologies Corp.

Non-limiting examples of components or portions of anaerobic systemsthat can be utilized in one or more configurations of the wastewatersystems include, but are not limited to, the DYSTOR® digester gas holdersystem, the CROWN® disintegration system, the PEARTH® digester gasmixing system, the PFT® spiral guided digester gas holder, the PFT®vertical guided digester holder, the DUO-DECK™ floating digester cover,and the PFT® heater and heat exchanger system, from Siemens WaterTechnologies Corp.

One or more embodiments pertinent to some aspects of the invention caninvolve a wastewater treatment system comprising a source of wastewaterto be treated and a sequencing batch reactor having a basin with a basininlet fluidly connectable to the source of the wastewater, an aerationsystem, a sludge collection system with a sludge outlet, and a decantingsystem with a supernatant outlet. The wastewater treatment system canalso comprise an anaerobic digester having a digester inlet fluidlyconnectable downstream from the sludge outlet, and a digested sludgeoutlet fluidly connectable to the basin inlet, and a controllerconfigured to generate a first output signal that provides fluidcommunication between the basin inlet and the source of wastewater, anda second signal that provides fluid communication between the sludgeoutlet and the digester inlet.

In still further embodiments of the invention, the methods andtechniques of the invention can comprise providing a wastewater to betreated and promoting biological sorption of the wastewater to betreated to produce a first mixed liquor. The methods and techniques ofthe invention can further comprise producing a solids-rich sludge and asolids-lean portion from the mixed liquor, and aerobically treating afirst portion of the solids-rich sludge to produce an at least partiallyaerobically treated sludge. A second portion of the solids-rich sludgecan be anaerobically digested to produce an anaerobically digestedsludge. The methods and techniques of the invention can even furthercomprise combining at least a portion of the at least partiallyaerobically treated sludge with the wastewater to be treated, andcombining at least a portion of the anaerobically digested sludge withthe wastewater to be treated.

In still further embodiments of the invention, the methods andtechniques of the invention can comprise providing a wastewater streamto be treated, and introducing the wastewater stream into a biologicalsorption tank to produce a first mixed liquor stream. The methods andtechniques of the invention can also comprise introducing the mixedliquor stream into a separator to produce a solids-rich stream and asolids-lean stream. The methods and techniques of the invention may evenfurther comprise introducing at least a portion of the solids-richstream into an aerobic treating tank to produce an at least partiallyaerobically treated stream. Even further, the methods and techniques ofthe invention can comprise at least a portion of the solids-rich streaminto an anaerobic digester to produce an anaerobically digested sludgestream. Still further, the methods and techniques of the invention cancomprise introducing at least a portion of the at least partiallyaerobically treated sludge stream into the biological sorption tank, andintroducing at least a portion of the anaerobically digested sludgestream into the biological sorption tank.

One or more embodiments pertinent to some aspects of the invention caninvolve a wastewater treatment system comprising a source of wastewaterto be treated and a biological treatment train fluidly connected to thesource of wastewater to be treated. The first treatment train cancomprise at least one biological reactor selected from the groupconsisting of an anaerobic reactor, an anoxic reactor, and an aerobicreactor. The wastewater treatment system can also comprise an anaerobicdigester fluidly connected downstream from a solids-rich outlet of thebiological treatment train and a digested anaerobic sludge recycle linefluidly connecting a digested sludge outlet of the anaerobic digesterand an inlet of the at least one biological reactor.

In still further embodiments of the invention, the methods andtechniques of the invention can involve or be directed to facilitatingwastewater treatment in a wastewater treatment system having abiological treatment train with at least one biological reactor selectedfrom the group consisting of an anaerobic reactor, an anoxic reactor,and an aerobic reactor. The method can comprise fluidly connecting asolids-rich outlet of the biological treatment train upstream of aninlet of an anaerobic digester, and fluidly connecting a digested sludgeoutlet of the anaerobic digester upstream of an inlet of the at leastone biological reactor.

The systems and components of the invention may also provide costadvantages relative to other wastewater treatment systems through use ofbiological processes in combination with anaerobic digestion. Thewastewater treatment processes of the present invention can reducesludge production through the use of various unit operations includingbiological processes and recycle streams. The wastewater treatmentprocesses also overcome some of the technical difficulties associatedwith use of anaerobic wastewater treatment processes, by, for example,concentrating or strengthening the sludge introduced into the anaerobicdigester. Additionally, costs associated with use of a conventionalaerobic stabilization unit are typically reduced because less aerationwould typically be required in the aerobic processes due to the use ofthe anaerobic digester and various recycle streams. The variousprocesses can also generate methane as a product of the anaerobicdigestion process, which can be used as an energy source. In certainembodiments, a large portion of the chemical oxygen demand (COD) andbiological oxygen demand (BOD) can be reduced using the anaerobicdigester. This can reduce the aeration and oxygen requirements, andthus, operation costs, and increase the amount of methane produced thatcan be used as an energy source. Additionally because anaerobicdigestion can be used to reduce COD and BOD in the sludge, the sludgeyield can also be reduced.

In contrast to conventional contact stabilization processes, wherein thesludge stabilization is performed in aerobic sludge stabilization tankswith retention times of a few hours such as between one and two hours,one or more of the present treatment systems can utilize a plurality ofsub-trains and one or more sorption systems that facilitate assimilationor biological sorption of suspended and/or dissolved materials. Forexample, the various systems and techniques disclosed herein canadvantageously provide wastewater treatment by utilizing a plurality ofsub-trains that have varied hydraulic loadings. A first train can treata majority of a sludge stream, preferably by anaerobic digestion, and asecond can train anaerobically treat a fraction of the sludge stream,typically only partially aerobically treated by exposure to aerobicactivity for less than full conversion or consumption of all oxygendemand. Various configuration of the present systems can utilizesolids/liquids separators that further reduce capital requirements.Thus, in some cases, one or more separators can be utilized to separatesludge or solids-rich streams to be treated in one or more of thesub-trains.

Some other embodiments of the treatment systems of the invention cancomprise collecting and/or converting various materials to produce asludge material. For example, biological sorption processes can beemployed to promote both adsorption and absorption processes thatfacilitate conversion of at least a portion of dissolved solids as wellas suspended solids in the water or wastewater. In the adsorptionprocess, ions and molecules of particles physically adhere or bond ontothe surface of another molecule or compound. For example, the adsorptionprocess can comprise attaching compounds or molecules to surfaces ofsoluble and insoluble particles in the wastewater to cause them tosettle in a downstream clarifier. In absorption processes, chemical andbiochemical reactions can occur in which compounds or substances in onestate are converted into another compound or substance in a differentstate. For example, compounds in the wastewater can be converted toanother compound, or can be incorporated by or into bacteria for thepurpose of growing new bacteria. Aeration can be provided to thebiological sorption process to mix and to provide an aerobicenvironment. The retention time in a biological sorption tank can bebetween a few minutes and a few hours, for example, between about fiveminutes and two hours, more preferably between thirty minutes and onehour. Aeration therein can be effected to provide mixing and maintain anaerobic environment that facilitates flocculation. Further flocculationor aggregation can be effected in the systems that utilize an aerobictreatment tank. In some cases, however, the aerobic treatment tankprovides substantially all the dissolved oxygen into the biologicalsorption tank.

In some cases, the treatment system can involve unit operations thathave various consortia of microorganisms that facilitate rapid return tosteady state conditions following an upset. For example, the treatmentsystem can circulate microorganisms that provide or facilitate anaerobicdigestive activity, such as methogenic activity.

In some previously known treatment systems, anaerobic digestion processfailures may result from a lack of methogenic activity to convert thebiomass acid and hydrogen to methane. The hydraulic residence time orsolids retention time of the anaerobic digester in these previouslyknown treatment systems are sometimes designed to be greater than thatof some embodiments of the presently disclosed treatment system. (Theanaerobic digesters in these previously known systems were sometimessized larger than in some embodiments of the presently disclosedtreatment system. A larger anaerobic digester size, for a given flowrate, would result in a greater hydraulic residence time or solidsretention time in the anaerobic digester.) In previously known systems,the anaerobic digester would be sized to maintain at least a steadystate bacterial population, taking into account the growth rates ofslower growing bacteria such as acetoclastic methanogens, with maximumspecific growth rate of about 0.3 day⁻¹ and hydrogenotrophic methanogenswith maximum specific growth rate of about 1.4 day⁻¹.

It was previously believed that methanogens were strict anaerobicbacteria that would die quickly in an aerobic environment. Variousaspects of the invention, however, involve treatment systems andsubsystems, unit operations, and components thereof that accommodate orincrease the survivability of methanogenic organisms. One advantageousfeature of the treatment systems of the present application involvesproviding a large amount of methanogens through the anaerobic recycle tothe contact stabilization process through the unique internal anaerobicsludge recycle path. At least a portion of the methanogenic bacteriareturn to the anaerobic digester, thereby seeding the anaerobic digesterwith methanogenic bacteria to join the existing population of the viablemethanogens in the anaerobic digester. This reduces the need for theanaerobic digester to have a size and resultant hydraulic residence timeor solids retention time to maintain a stable methanogenic bacteriapopulation in the absence of bacterial seeding, as in previously knownprocesses.

The concentration of seeding methanogenic bacteria, on a basis of acount of microorganisms, provided at the input of the anaerobic digestermay in some embodiments be at least a target percentage, such as about10% or more, of the concentration of the methanogenic bacteria presentin the anaerobically digested sludge stream exiting the anaerobicdigester. In some embodiments, this percentage may be, for example, 25%or more, 33% or more, 50% or more, or 75% or more. In some embodiments,the concentration of methanogenic bacteria provided at the input of theanaerobic digester may be a substantial fraction of the concentration ofthe methanogenic bacteria present in the anaerobically digested sludgestream exiting the anaerobic digester, for example, about 10% or more,about 30% or more, about 40% or more, or about 50% or more.

The anaerobic digester of systems in accordance with the present may besized smaller than those in previously known systems. The methanogenicbacterial seeding of the anaerobic digester also provides for a safetyfactor against disruptions of the anaerobic digestion process. In theevent of anaerobic digestion process upset or failure, the anaerobicdigesters of the presently disclosed systems would recover faster thanthat the anaerobic digesters in previously known systems because theseeding of the anaerobic digester with methanogenic bacteria would addto the rate replenishment of methanogenic bacteria in the anaerobicreactor due to the growth of these bacteria therein, reducing the timerequired for the anaerobic digester to achieve a desired concentrationof methanogenic bacteria.

The advantage of methanogen recycle can be estimated as follow:

$\theta_{x} = \frac{X_{a}V}{{QX}_{a} - {QX}_{a}^{0}}$

Where

-   -   θ_(x)=Solids retention time in anaerobic digester (days)    -   X_(a)=concentration of methanogens    -   Q=influent and effluent flow rate    -   X_(a) ⁰=concentration of methanogens in the inlet stream, which        is normally considered zero for conventional activated sludge        process.

If about 50% of methanogens survive in the short solid retention timecontact stabilization process and recycled back to anaerobic digester,the solids retention time of the anaerobic digester could be doubled, orthe size of the anaerobic digester decreased by half. For example, inpreviously known systems a hydraulic retention time in an anaerobicdigester was in many instances set at between about 20 and about 30days. With a treatment system operating in accordance some embodimentsof the present application, this hydraulic retention time may be reducedby about 50% to between about 10 and about 15 days.

In some embodiments of the apparatus and methods disclosed herein, ahydraulic retention time in a treatment system contact stabilizationvessel may be about one hour or less. A significant portion ofmethanogens can be recycled in the short solid retention time contactstabilization aerobic process, which can reduce the capital cost andoperational cost of the anaerobic digesters. For example, the tankvolume of the anaerobic digesters could be decreased to bring the safetyfactor to a range closer to those anaerobic digesters without amethanogen recycle process. With smaller volume, the capital cost of theanaerobic digesters and the mixing energy consumption of the anaerobicdigestion process would both decrease, which will make apparatus andprocesses in accordance with the present disclosure more cost effectivethan previously known apparatus and processes.

In other embodiments, the seeding of the anaerobic digester withrecycled methanogenic bacteria may provide for decreasing the hydraulicresidence time of sludge treated in the digester. This would result in adecreased cycle time, and thus an increased treatment capacity of thetreatment system. Increasing the amount of methanogens recycled to theanaerobic digester, by, for example, increasing an amount of methanogenscontaining sludge directed into the digester, would provide greateropportunity to decrease the hydraulic residence time in the digester andincrease the treatment capacity of the system.

In some embodiments an amount of methanogenic bacteria recycled to theinlet of the anaerobic digester may be further increased by, forexample, decreasing the solids retention time in the contractstabilization process by increasing the anaerobic sludge recyclepercentage. The anaerobic sludge recycle may include solids-rich sludgedirected from the clarifier 114 to the thickener 124, as shown in theembodiment illustrated in FIG. 1. Alternatively, or additionally, theorganic loading rate of the bio-sorption unit may be increased. When theorganic loading rate is high, available oxygen could be quickly used inthe outer layer of the biological floc as the result of higher oxygenutilization rate in the outer layer of the floc, leaving an anoxic oranaerobic “core” in the floc to protect methanogens. Also, in someembodiments, the dissolved oxygen in the contact tank and/orstabilization tank may be reduced to decrease the oxygen transferdriving force. This may further help to create anoxic or anaerobic“core” in the floc that mat may protect methanogens.

If a significant portion of methanogens can be recycled in the aerobiccontact stabilization process, the capital cost and operational cost ofthe anaerobic digesters (ADs) could be decreased. For example, the tankvolume of the ADs could be decreased to bring the safety factor to arange closer to those ADs in systems not including a methanogen recycleprocess. With smaller volume, the capital cost of ADs and the mixingenergy consumption of AD will both decrease, which will make the hybridprocess more cost effective.

In certain embodiments, the biological sorption tank is constantlyseeded with nitrification bacteria (such as ammonia oxidizing andnitrite oxidizing biomass) which can survive the anaerobic digester andwhich can be recycled back to the aerobic environment. For example,nitrification and de-nitrification can take place in the biologicalsorption tank. Nitrification may be carried out by two groups ofslow-growing autotrophs: ammonium-oxidizing bacteria (AOB), whichconvert ammonia to nitrite), and nitrite-oxidizing bacteria (NOB), whichoxidize nitrite to nitrate. Both are slow growers and strict aerobes. Insome embodiments of treatment systems disclosed herein, thenitrification bacteria are introduced to and/or grown in a biosorptiontank, where they are captured in the floc. Some of the nitrificationbacteria will pass out from the bio-sorption tank and be sent to ananaerobic digester.

It was previously believed that the strictly anaerobic conditions of theanaerobic digester would kill the nitrification bacteria. Variousaspects of the invention, however, involve treatment systems andsubsystems, unit operations, and components thereof that accommodate orincrease the survivability of nitrification organisms in anaerobic andanoxic conditions that may occur in some biological nutrient removalprocesses. Nitrification bacteria which survive the anaerobic digesterand are returned to the aerobic part of the treatment process mayenhance the nitrification process performance in ways that can lowercapital costs, for example by providing for a reduced aerobic treatmentvessel size and/or reduced aerobic treatment hydraulic retention timeand/or an increased safety factor that would render the nitrificationprocess more stable in response to disruptions to the treatment process.Disruptions to the treatment process encompass deviations from desiredoperating parameters which may be caused by, for example, interruptionsin flow of material through the treatment system or a loss oftemperature control at one or more unit operations. The survival rate ofnitrification bacteria in an anaerobic digester could be increased bydecreasing a hydraulic residence time in the anaerobic digester, whichwould be accomplished if the anaerobic digester were seeded withrecycled methanogens, as described above.

In certain embodiments of the invention, sludge processed through anaerobic treatment and/or an anaerobic digester may also enter thebiological sorption tank as a recycle stream to assist in the biologicalsorption processes. Other processed streams, such as a solids-leanportion or a sludge-lean portion exiting a thickener or clarifier, or amixed liquor produced from a polishing unit can also be introduced as arecycle stream to the biological sorption tank to assist in thebiological sorption process.

In other cases, some configurations can involve chemically facilitatedsorption mechanisms.

Some embodiments of the treatment processes of the invention cancomprise biologically treating at least a portion of the sludge from thewastewater to be treated. Biological treatment processes can be used toremove and/or biodegrade undesirable materials in the water to betreated, for example, organic pollutants. In certain embodiments, thebiological treatment processes can be aerobic biological treatmentprocesses. Depending on the operating conditions, at least a portion ofthe organic material in the water to be treated or sludge can beoxidized biologically and converted to carbon dioxide and water. Incertain embodiments, the reduction in oxygen demand can be as high asabout 80-90%. In some embodiments, the a portion of the organic materialin the water to be treated or sludge can be reduced only partially byutilizing a less than sufficient aeration rate or a less than sufficientresidence time. For example, the reduction in oxygen demand can be lessthan 70%, less than 50%, less than 30%, or less than 10%. Inparticularly preferred embodiments, the reduction in oxygen demand canbe less than 8%, and more preferably between about 0.08% to about 6%.The water to be treated or sludge can be aerated and mixed for a periodof time in, for example, an open tank using air diffusers or aerators.Aerobic biological treatment processes can be performed to provide adissolved oxygen content of from about 0.2 mg/L to about 5 mg/L, or insome embodiments, from about 1.5 mg/L to about 2.5 mg/L. Retention timein the aerobic treatment tank can be several weeks, or in someembodiments, in a range of from about one to about six hours, and insome embodiments, in a range of from about one to about two hours.

Some embodiments of the treatment systems of the invention can comprisea system capable of breaking down and/or converting various materialsinto other, more useful, end products. In this system, microorganismscan break down biodegradable material in the absence of oxygen. In thisanaerobic digestion process, many organic materials can be processed,such as waste paper, grass clippings, food, sewage, and animal waste.This process has the advantage of providing volume and mass reduction ofthe sludge being introduced into the system. The process can produce amethane and carbon dioxide rich biogas suitable for energy production.The anaerobic digestion process can comprise bacterial hydrolysis of thesludge being introduced into the digester which can break down insolubleorganic polymers such as carbohydrates into sugars, amino acids, andfatty acids. In certain anaerobic digesters, acidogenic bacteria canthen convert these intermediate materials into carbonic acids, alcohols,hydrogen, carbon dioxide, ammonia, and organic acids. The compoundsconverted by the acidogenic bacteria can be further digested byacetogenic microorganisms to produce acetic acid, carbon dioxide, andhydrogen. Methanogenic bacteria or methanogens can then convert thecarbon dioxide, hydrogen, ammonia, and organic acids to methane andcarbon dioxide. The methane produced from this anaerobic digestionprocess can be used as an energy source. In some embodiments, a greaterconcentration of methanogenic bacteria present in the anaerobicdigester, or a greater amount of methanogenic bacteria recycled into theanaerobic reactor may result in a greater amount of methane produced.

In certain embodiments, the anaerobic digester is constantly seeded witha consortium of methanogens that reside in the sludge of the treatmentprocess. Certain slow growing anaerobic bacteria such as acetoclasticmethanogens and hydrogentrophic methanogens can survive in the aerobicenvironment of the present invention, and will return to the anaerobicdigester allowing the anaerobic digester to be constantly seeded with anontrivial level of methanogens. This allows for a more reliabletreatment process, and allows for a smoother transition back to a steadystate if a problem, such as a disruption in flow of material, occurswithin the system. The seeding of the anaerobic digester may also, asdiscussed above, increase an amount of methane produced in the anaerobicdigester.

The anaerobic digestion process can be operated at temperatures between20° C. and 75° C., depending on the types of bacteria utilized duringdigestion. For example, use of mesophilic bacteria typically requiresoperating temperatures of between about 20° C. and 45° C., whilethermophilic bacteria typically require operating temperatures ofbetween about 50° C. and 75° C. In certain embodiments, the operatingtemperature may be between about 25° C. and about 35° C. to promotemesophilic activity rather than thermophilic activity. Depending on theother operating parameters, the retention time in an anaerobic digestercan be between about seven and about fifty days retention time, and insome embodiments, between about fifteen and about thirty days retentiontime. In certain embodiments, the reduction in oxygen demand can beabout 50%.

In certain embodiments, the sludge that is processed through theanaerobic digester may be recycled back to an inlet of a biologicalsorption process. Prior to recycling the anaerobically digested sludgeinto the biological sorption process, the anaerobic sludge may beprocessed through an aerobic conditioning tank to modify thecharacteristics of the anaerobically digested sludge. In certainembodiments, the anaerobically digested sludge may also be introducedinto the inlet of the aerobic treatment tank to combine with thesolids-rich sludge entering the aerobic treatment tank.

Some other embodiments of the treatment system can comprise one or moresystems capable of separation processes. The separation processes mayseparate certain portion of water to be treated or sludge. Theseparation processes may be capable of removing large materials fromwastewater, for example, grit, sand, and gravel. Other separationsprocesses can remove large insoluble material of the water to be treatedsuch as, but not limited to fats, oils, and grease. Other separationsystems may take advantage of the settling characteristics of materials,such as settleable solids and floating bodies. Various separations mayemploy unit operations such as settling tanks, clarifiers, thickeners,and filtration systems.

Some other embodiments of the treatment system can comprise one or morerecycle streams that may deliver the output of a first unit operation tothe inlet of a second unit operation upstream of the first unitoperation. In certain embodiments, the output from an anaerobicdigester, an aerobic digester, a sludge thickener, or an aerobicpolishing unit can be recycled to the input of the primary clarifier orthe biological sorption tank. In other embodiments, the output of ananaerobic digester can be recycled to the input of the aerobic treatmenttank.

Some other embodiments of the treatment system can comprise a sequencingbatch reactor that is fluidly connected or connectable to a source ofwastewater to be treated. The sequencing bioreactor may biologicallytreat the wastewater by promoting degradation or conversion ofbiodegradable material, followed by settling and/or decanting the mixedliquor comprising the converted material. The sequencing batch reactorcan be fluidly connected or connectable to an anaerobic digester locateddownstream from the reactor.

FIG. 1 exemplarily illustrates an embodiment in accordance with someaspects of the invention. The treatment system 10 can be fluidlyconnected or connectable to a source 110 of water to be treated. Inaccordance with any one of the aforementioned aspects of the invention,treatment system 10 can comprise one or more treatment unit operations,which may include one or more biological treatment processes and one ormore solids-reducing and solids-collecting systems or processes.

Source 110 of water to be treated can be a water collection system fromany one or more of a municipality, a residential community, and anindustrial or a commercial facility, and an upstream pre-treatmentsystem, or combinations thereof. For example, source 110 can be asedimentation or settling tank receiving water from a sewer system.

Treatment system 10 can comprise one or more biological sorption tanks112 that promote aggregation of at least a portion of dissolved andsuspended solids contained therein. Biological sorption tank 112 cancomprise or is configured to contain a biomass of microorganisms thatcan metabolize biodegradable materials in the water to be treated. Forexample, biological sorption tank 112 can comprise or is configured tocontain a biomass of microorganisms that processes biodegradablematerials in the water to be treated through absorption of thebiodegradable materials. Biological sorption tank 112 can also compriseor is configured to contain substances or compounds for promotion ofadsorption of soluble and insoluble material, such as organic compounds,in the wastewater or water to be treated. The biological sorptionprocess may include aeration and mixing to help maintain the aerobicenvironment within biological sorption tank 112.

The biological sorption tank 112 produces a first mixed liquor 212 whichcan be introduced into a separator such as clarifier 114 to produce asolids-lean stream 214 and a solids-rich sludge 216. The solids-leanstream 214 can be processed further, for example, to render the at leastpartially treated water to be suitable for discharge, in a polishingunit 118, to produce treated product 120, which can be suitable forother uses, and also a second mixed liquor 222, which can be recycledback to source of wastewater 110 or to the sorption tank 112.

Solids-rich sludge 216 can be divided allowing at least a portion ofsolids-rich sludge 216 to be aerobically treated in an aerobic treatmenttank 116 to produce an at least partially aerobically treated stream224. At least partially aerobically treated stream 224 can be recycledback to source of wastewater to be treated 110, combined therewith, orintroduced into other unit operations of the treatment system.

At least a portion of solids-rich sludge 216 can be introduced to ananaerobic digester 122 to produce an anaerobically digested sludge 226.A portion of the anaerobically digested sludge 226 can be disposed of asa waste sludge 130. A portion of the anaerobically digested sludge 226can also be recycled back to the source of wastewater 110, combinedtherewith, or introduced into other unit operations of the treatmentsystem.

Optionally, prior to introducing at least a portion of the solids-richsludge 216 to the anaerobic digester 122, at least a portion of thesolids-rich sludge 216 can be introduced to a thickener 124 to produce athickened sludge 228 and a sludge-lean portion 232. The thickened sludge228 can then be introduced into the anaerobic digester 122 and thesludge-lean portion 232 can be recycled back to the source of wastewater110, combined therewith, or introduced into other unit operations of thetreatment system.

Any portion between zero and 100 percent of the solids-rich sludge 216can be introduced into the aerobic treatment tank 116, the remainderbeing directed to the anaerobic digester. In certain examples, theportion introduced into the thickener 124 or the anaerobic digester 122can be between about two and about twenty percent of the solids-richsludge 216. In other examples, the portion of the solids-rich sludge 216introduced into the thickener 124 or the anaerobic digester 122 can bebetween about four and about eight percent of the solids-rich sludge216.

In certain examples, the treated product 120 can be monitored fordissolved solids content, COD/BOD, or other identified characteristics.If the level of any one identified characteristic is not within adesired range or at a desired level, adjustments can be made to thetreatment system. For example, if the COD of the treated productdeviates from a desired level or acceptable range, a greater or lesserportion of anaerobically treated sludge 226 can be discharged as wastesludge 130.

FIG. 2 exemplarily illustrates another embodiment in accordance withsome aspects of the invention. A treatment system 30 can be fluidlyconnected to a source 310 of water to be treated. In accordance with anyone of the aforementioned aspects of the invention, the treatment system30 can comprise one or more treatment unit operations, which may includeone or more biological treatment processes and one or moresolids-reducing and solids-collecting systems or processes.

The system 30 can have one or more primary separators. For example, aprimary clarifier 311 fluidly connected to a source 310 of water to betreated can be utilized to allow settling of at least a portion ofcomponents of the source 310 of water to be treated so that solids-leanwastewater 411 can be produced and introduced to a biological sorptiontank 312. The primary clarifier 311 can also produce a solids-richwastewater stream 413 which may be combined with a solids-rich sludge416 or thickened sludge 428 to be introduced into an anaerobic digester322, discussed in more detail below. The separators of the system thatcan be utilized, including but not limited to the primary separator,include filters and dissolve air flotation type units, with or withoutgrit removal.

Solids-lean wastewater 411 is typically introduced into the biologicalsorption tank 312 to produce a first mixed liquor 412 which can beseparated in another separator, such as a clarifier 314, to produce asolids-lean stream 414 and solids-rich sludge 416. The solids-leanstream 414 can be processed further using, for example, a tertiary orpost-treatment train with, for example, a membrane bioreactor 318 toproduce a treated product 320 which can be suitable for other uses. Asecond mixed liquor 422 produced from membrane bioreactor 318 can berecycled back to be combined with the solids-lean wastewater 411, orintroduced into other unit operations of the treatment system.

The solids-rich stream 416 can be divided, allowing at least a portionof the solids-rich stream 416 to be aerobically treated in aerobictreatment tank 316 to produce an at least partially aerobically treatedstream 424. The at least partially aerobically treated stream 424 can berecycled back to be combined with solids-lean wastewater 411.

At least a portion of the solids-rich sludge 416 can be introduced tothe anaerobic digester 322 to produce anaerobically digested sludge 426.A portion of the anaerobically digested sludge 426 can be disposed of aswaste sludge 330. A portion of the anaerobically digested sludge 426 canalso be recycled back to be combined with the solids-ridge sludge 416 tobe introduced to the aerobic treatment tank 316.

Prior to introducing at least a portion of the solids-rich sludge 416 tothe anaerobic digester 322, at least a portion of the solids-rich sludge416 can be introduced to a thickener 324 to produce a thickened sludge428 and a sludge-lean portion 432. The thickened sludge 428 can then beintroduced into the anaerobic digester 322 and the sludge-lean portion432 can be recycled back to be combined with the solids-lean wastewater411.

Any portion between zero and including 100 percent of the solids-richsludge 416 can be introduced into the aerobic treatment tank 316, theremainder being directed to the anaerobic digester. In certain examples,the portion introduced into the thickener 324 or the anaerobic digester322 can be between about 2 and about 20 percent of the solids-richsludge 416. In some cases, however, a portion of the solids-rich sludge416 can be discharged as waste sludge 330.

In certain examples, treated product 320 can be monitored for dissolvedsolids content, COD/BOD, or other identified characteristics. If thelevel of any one identified characteristic is not within a desired rangeor at a desired level, adjustments can be made to the treatment system.For example, if the COD of the treated product 330 differs from adesired level, a greater or lesser portion of anaerobically treatedsludge 426 can be discharged as waste sludge 330.

One or more nitrification units can be utilized. For example, a biofilmnitrification unit, which can be, for example, a moving bed bioreactor,can be disposed to receive at least a portion of the solids-lean streamfrom the separator 314. Effluent from the nitrification unit can bemixed with sludge from a clarifier to effect at least partialde-nitrification. Re-aeration can then be performed to remove at least aportion of nitrogen as a gas. Such variations can reduce or eliminatethe use of external carbon sources.

FIG. 3 exemplarily illustrates another embodiment in accordance withsome aspects of the invention. The treatment system 50 can be fluidlyconnected or connectable to a source 510 of water to be treated. Inaccordance with any one of the aforementioned aspects of the invention,the treatment system 50 can comprise one or more treatment unitoperations, which may include one or more biological treatment processesand one or more solids-reducing and solids-collecting systems orprocesses.

An optional primary clarifier 511 can be fluidly connected orconnectable to the source 510 of water to be treated. The primaryclarifier 511 typically produces solids-lean wastewater 611 andsolids-rich wastewater 613. At least a portion of the solids-leanwastewater 611 can be introduced into one or more sequencing batchreactors 512, wherein one or more treatment steps can be performed. Forexample, the sequencing batch reactor 512 can operate in one or morestages to treat the water or wastewater to be treated in a desiredmanner.

The sequencing batch reactor 512 can be operated or configured toreceive the water to be treated from the source 510 in a first stage,which is typically referred to as a FILL stage. The FILL stage can beperformed in aerated, anoxic or a combination of aerated and anoxicconditions. In some embodiments, the influent water to be treated isintroduced into a basin (not shown) of the sequencing batch reactor 512through one or more influent distribution manifolds. The basin can besized to accommodate or provide a desired hydraulic retention time andto accommodate the volume and incoming flow rate of water to be treated.

When the basin of the sequencing batch reactor 512 is at least partiallyfilled or thereafter, the sequencing batch reactor 512 can be operatedto favor bacterial metabolic activity that converts or treats at least aportion of biodegradable material in a second stage, which is typicallyreferred to as a REACT stage. The REACT stage, which can be performed inone or more discrete steps or stages, can also be operated to performother processes, such as biological sorption processes. In some cases,however, biological sorption may have been or be completed in the FILLstage. The REACT stage can be performed under aerobic conditions byintroducing oxygen, preferably as air, from one or more air sources (notshown) through one or more aeration manifolds that are typicallysubmerged in the liquor. The one or more REACT stages, which can beperformed, for example, after the FILL stage and/or after other stages,such as after a DECANT stage, can be performed for a period sufficientto promote at least partial biodegradation or at least conversion, suchas by biological sorption, for a period sufficient to promote adsorptionand absorption of suspended particles and soluble material. For example,aeration can be performed through an aeration system (not shown) in thebasin to create aerobic conditions to facilitate oxidation of ammonia tonitrate by nitrification bacteria. An air source preferably furtherprovides air released through the aeration manifold of the aerationsystem as air bubbles in amounts sufficient to induce mixing of theliquor within the basin of the sequencing batch reactor 512.Alternatively, or in conjunction with the aeration induced phenomena,mixing can also be effected by a mixer, such as an impeller, which maybe advantageous when mixing is desired without introducing air into theliquor. The one or more REACT stages is not limited to the use of airand any source of oxygen that provides a target dissolved oxygenconcentration in the liquor can be utilized for each or any of the oneor more of REACT stages. The one or more REACT stages can include anaeration stage and a separate re-aeration stage that occurs at someperiod after the aeration stage.

A SETTLE stage typically follows the at least one aeration, biologicalsorption and/or mixing stages to create quiescent conditions that allowat least a portion of the biomass in the liquor to settle to form asupernatant, a solids-lean liquor, and a solids-rich or sludge layerbelow the supernatant. The duration of the SETTLE stage may vary anddepend on several factors including, but not limited to, the temperatureof the mixed liquor and the nature and composition of the biomass.

The solids-lean liquor 614 can then be withdrawn or decanted in a DECANTstage and can be further treated in, for example, a polishing unit 518.At least a portion of the settled sludge can be withdrawn through amanifold (not shown) and directed to further treatment by variousbiological processes or disinfection treatments. At least a portion ofthe sludge layers, as a solids-rich stream 616, can be withdrawn andintroduced to various other biological processes, such as by aerobictreatment or anaerobic digestion in an anaerobic digester 522 (discussedbelow). Withdrawal or decanting of the treated effluent or solids-leanliquor 614 can be performed utilizing a decanting system (not shown) inthe basin, which typically has a floating solids-excluding decanter orskimmer (not shown) that may be constructed to have apertures that donot or at least reduce the likelihood of turbulent conditions thatdisturb the settled solids-rich layer during withdrawal of thesolids-lean supernatant.

An IDLE stage may be optionally included during instances the sequencingbatch reactor 512 waits to receive influent to be treated.

In some instances, any of the functions or activities can be performedin more than one stage. For example, withdrawing solids-rich sludgestream 616 can be performed during the SETTLE stage as well as duringthe IDLE stage. Thus, the invention can be practiced in other than thesequence of stages presented herein. Further, any one or more stages canbe omitted or combined. For example, in some cases, the REACT stage canbe performed during the FILL stage thereby allowing combining orextending the duration of the REACT stage.

The OMNIFLOW® sequencing batch reactor system from Siemens WaterTechnologies Corp. is an example of a commercially available treatmentsystem that can comprise the biological train used to effect biologicalnutrient removal in accordance with some aspects of the invention.Further aspects of the invention may utilize the systems and methodsdisclosed by any of Calltharp and Calltharp et al. in U.S. Pat. Nos.4,775,467, 5,021,161, and 6,884,354, each of which is incorporatedherein by reference for all purposes. Indeed, some advantageous featurespertaining to constant level sequencing batch reactor systems may beutilized. Such constant level biological conversion systems mayadvantageously provide even further improved process control of theoverall treatment system by reducing any operational fluctuations orvariations during downstream filtration operations. Further advantagescan, in some cases, reduce the size of any equalization tanks, or eveneliminate the need for such unit operations, which reduces the overalltreatment system footprint and capital requirements.

Sequencing the various stages of the treatment system may be facilitatedby utilizing one or more controllers 534 operatively coupled to the oneor more sequencing batch reactors 512, the primary clarifier 511, thepolishing unit 518, the thickening unit 524, and the anaerobic digester522. One or more sensors (not shown) may be utilized in or with the oneor more unit operations, such as the sequencing batch reactor 512, toprovide an indication or characteristic of the state or condition ofprocesses during the treatment processes. For example, one or more levelindicators (not shown) can be disposed in the basin of the sequencingbatch reactor 512 and configured to transmit to one or more controllers534 a representation of the liquid level contained within the basin. Thecontroller 534 can, based on the signals received from the one or moresensors, generate and send control signals to any of the components ofthe primary clarifier 511, the polishing unit 518, the thickening unit524, and the anaerobic digester 522, or other components or subsystemsof the treatment system 50. For example, at a high liquid levelcondition in the basin, as measured by the one or more level indicators,the controller 534 can generate and transmit a control signal to anactuator that closes an inlet valve (not shown) fluidly isolating thesource 510 and the basin of the sequencing batch reactor 512. Thecontroller 534 may further generate control signals that initiate andterminate the stages of the one or more sequencing batch reactors 512.For example, the controller 534 can generate and transmit a controlsignal to energize or de-energize the air source for the sequencingbatch reactor 512.

The solids-lean stream 614 decanted from the sequencing batch reactor512 can be further treated in a polishing treatment system. For example,one or more configurations of the treatment systems as disclosed hereincan comprise one or more polishing units 518 using treatment processesincluding, but not limited to biological nitrification/denitrificationand phosphorus removal, chemical oxidation, chemical precipitation, andseparation systems including dissolved inorganic solids removal by ionexchange, ultrafiltration, reverse osmosis, ultraviolet radiation, orelectrodialysis. Treated product 520 from unit 518 can be delivered tostorage, to a secondary use, or discharged to the environment.

The solids-rich sludge 616 can be further processed in the anaerobicdigester 522 to produce an anaerobically digested stream 626.

During operation of the treatment system, one or more targetcharacteristics can be utilized to regulate one or more operatingparameters of any of the unit operations of the system.

A portion of the anaerobically digested stream 626 can be recycled to becombined with the source of wastewater to be treated 510 or thesolids-lean wastewater 611. A portion of the anaerobically digestedstream 626 can also be discarded from the system 50 as waste sludge 530.

Optionally, prior to introducing at least a portion of the solids-richsludge 616 to the anaerobic digester 522, at least a portion of thesolids-rich sludge 616 can be introduced to a thickener 524 to produce athickened sludge 628 and a sludge lean portion 632. The thickened sludge628 can then be introduced into the anaerobic digester 522 and thesludge-lean portion 632 can be recycled back to the source of wastewater510 and/or solids-lean wastewater 611, combined therewith, or introducedinto other unit operations of the treatment system.

Another embodiment of a system configured to circulate microorganisms,for example, methanogenic bacteria and/or nitrification bacteria, isschematically illustrated in FIG. 10. The system 70 includes awastewater inlet 810 which feeds a sequencing batch reactor 812, whichmay include, for example, a biological sorption tank. A clarifier 814,or other form of separator, such as a hydrocyclone or settling tank, istypically located downstream of the sequencing batch reactor 812. Theclarifier 814 is typically configured to produce a solids-lean effluentto an effluent output 820, which may be further processed by, forexample, one or more polishing operations to produce water that may beused for potable or non-potable purposes. A sludge thickener 824 islocated downstream of a solids-rich outlet of the clarifier 814. Alsofluidly connected to the solids-rich outlet of the clarifier 814 is astabilization tank 818, which in some embodiments may comprise anaerobic treatment tank. In some embodiments, a greater amount of thesolids-rich output from the clarifier 814 is directed to thestabilization tank 818 than to the sludge thickener 824. In someembodiments about 80% or more, for example greater than about 90% orgreater than about 95% of the solids-rich output from the clarifier 814is directed to the stabilization tank 818. An anaerobic digester 822 islocated downstream of a solids-rich sludge output of the sludgethickener 824. A sludge-lean output of the sludge thickener 824 maydirect a solids-lean fluid to the stabilization tank 818. The anaerobicdigester 822 produces anaerobically digested sludge, at least a portionof which may be directed to the stabilization tank 818. A portion of thedigested sludge from the anaerobic digester may also be directed to awaste sludge outlet 830 for further treatment or disposal. An outlet ofthe stabilization tank 818 feeds back into the sequencing batch reactor812.

A precipitation rector may be included in any of the systems disclosedherein to precipitate out one or more desired compounds for example,phosphorous and/or nitrogen from one or more streams from the system.One example of a system utilizing a precipitation reactor is theembodiment of an activated sludge treatment system 80 illustrated inFIG. 11. Wastewater from a wastewater inlet 910 is directed to a firsttreatment tank 911, which may comprise, for example, an anaerobicdigestion vessel. Anaerobically treated wastewater is directed from anoutlet of the treatment tank 911 to an inlet of an aerobic treatmenttank 912. The aerobically treated wastewater is then conveyed from theaerobic treatment tank 912 to a first clarifier 914. The clarifier 914separates the aerobically treated wastewater into a solids-lean portionwhich is directed to an outlet 920 from which it may be directed tofurther downstream processes for further treatment. A portion of asolids-rich output from the clarifier 914 may be recycled back to thetreatment tank 911, and a second portion of the solids-rich output fromthe clarifier 914 may be directed to a second clarifier 915. A portionof a solids-lean output stream from the second clarifier 915 may berecycled back to the treatment tank 911, while a second portion of thesolids-lean output stream from the second clarifier 915 is directed to aseparator 926, which may comprise a membrane filtration unit. Theportion of the solids-lean output stream from the second clarifier 915directed to the separator 926 may be utilized to help wash precipitatesand/or retained sludge from the separator 926. In some embodiments,wherein the separator 926 comprises a membrane filter, at least aportion of the solids-lean output stream from the clarifier 915 may beused to backwash a membrane of the membrane filter. The backwash couldbe initiated based on a measurement of a transmembrane pressure acrossthe membrane or on a time basis.

A solids-rich output stream from the clarifier 915 is directed to ananaerobic digester 922. Anaerobically digested sludge output from theanaerobic digester 922 is directed to the separator 926. The separator926 produces a solids-rich output stream, a portion of which may bedirected to a waste sludge outlet 930, and a second portion of which maybe recycled back to the treatment tank 911. A solids-lean output streamfrom the separator 926 is directed to a mineral extraction process, forexample to a reactive precipitation reactor 940 such as the CONTRAFAST®High-Rate Sludge Thickener Clarifier, available from Siemens WaterTechnology Corp.

The precipitation reactor may be utilized to precipitate out phosphorousand/or nitrogen containing compounds, for example struvite(MgNH₄PO₄.6H₂O), by the addition of precipitating agents, such as amagnesium salt (e.g., magnesium chloride) in the precipitation reactorin accordance with the reaction below.Mg²⁺+NH₄ ⁺+PO₄ ³⁻+6H₂O→MgNH₄PO₄.6H₂O

In some applications, it would be beneficial to utilize a precipitationagent such as a magnesium salt to precipitate out the phosphorous andnitrogen in the precipitation reactor rather than, for example, aluminumor iron. The precipitation agent may be supplied from a source ofprecipitation agent 950 which in some embodiments may be external to theprecipitation reactor 940, and in other embodiments may be includedwithin the precipitation reactor 940. Struvite may be used as afertilizer, and thus may be an agriculturally useful precipitate.Precipitating phosphorous in the precipitation vessel using aluminum mayproduce an aluminum phosphate precipitate, which is unsuitable for useas a fertilizer, and thus would not be as agriculturally valuable asstruvite. Similarly, precipitating phosphorous with iron may produceiron phosphate, which is also unsuitable for use as a fertilizer. Inother embodiments, one or both of aluminum phosphate and/or ironphosphate may be precipitated from a solids-lean output stream from theseparator 926 for use in other applications.

A pH adjuster, such as ammonium hydroxide, magnesium hydroxide, anothercaustic, or an acid may also be added to the solids-lean output streamin the precipitation reactor to control an Mg²⁺ concentration and/or pHto within desired ranges. The pH adjuster may be supplied from a sourceof pH adjuster 955 which in some embodiments may be external to theprecipitation reactor 940, and in other embodiments may be includedwithin the precipitation reactor 940. In some embodiments theprecipitation reaction may take place at a temperature in a range offrom about 20° C. to about 40° C., or in some embodiments from about 25°C. to about 35° C. at a pH of between about 6 and about 12, in someembodiments between about 7.5 and about 11, and in some embodiments,between about 8.5 and about 10. In some embodiments, after precipitationof struvite the phosphorous-lean liquid may be recycled back to theactivated sludge treatment system. In some embodiments thephosphorous-lean liquid may be pH adjusted to a pH of, for example,about 7 by the introduction of a pH adjuster, for example, an acid or abase from a source of pH adjuster 945 prior to being recycled back tothe activated sludge treatment system. In other embodiments, thephosphorous-lean liquid recycled back to the activated sludge treatmentsystem may be allowed to maintain an alkaline pH, or be pH adjusted toan alkaline pH. The alkalinity may in some embodiments assist in anitrification process performed in the activated sludge treatmentsystem.

The amount of precipitating agent (e.g., magnesium chloride) may bedetermined based on an analysis of the concentration of phosphorousand/or nitrogen in the solids-lean stream directed into theprecipitation reactor. In some embodiments, the precipitating agent maybe added in a stoichiometric ratio to phosphorous or nitrogen present inthe solids-lean stream, e.g., one molecule of magnesium for eachmolecule of phosphorous or nitrogen in the solids-lean stream. In otherembodiments, a slightly higher, for example about 10% higher, thanstoichiometric ratio of precipitation agent to phosphorous or nitrogenin the solids-lean stream may be added. In other embodiments, less thana stoichiometric ratio may be added.

The various systems and techniques disclosed herein can significantlyreduce energy consumption, or even provide energy, and also reduce theamount of sludge produced during wastewater treatment.

Further, a controller can facilitate or regulate the operatingparameters of the treatment system. For example, a controller may beconfigured to adjust a rate of recycle of the one or more streams, aduration of one or more residence times, a temperature, and/or adissolved oxygen concentration in a fluid in any of the unit operationsof the treatment system.

The controller may respond to signals from timers (not shown) and/orsensors (not shown) positioned at any particular location within thetreatment system. For example, a sensor positioned in the anaerobicreactor may indicate less than optimum conditions therein. Further, theone or more sensors may monitor one or more operational parameters suchas pressure, temperature, one or more characteristics of the liquor,and/or one or more characteristics of any of the effluent streams.Similarly, a sensor disposed in or otherwise positioned with any of therecycle streams can provide an indication of a flow rate thereof at,below, or above a desired or target rate. The controller may thenrespond by generating a control signal causing an increase or decreasein the recycle flow rate. The target recycle flow rate of the mixedliquor from the polishing sub-train may be dependent on an operatingparameter of the treatment system. For example, the target recycle flowrate may be a multiple of, e.g., at least two times, the influent flowrate of the incoming water to be treated. In some cases, the solidsdischarge rate may be adjusted to achieve one or more targetcharacteristics of the treated water. Other control schemes may involveproportionally varying the relative flow rates between the anaerobicdigester and the aerobic treatment tank based at least partially on theoxygen demand of the influent or water to be treated.

The system and controller of one or more embodiments of the inventionprovide a versatile unit having multiple modes of operation, which canrespond to multiple inputs to increase the efficiency of the wastewatertreatment system.

The controller may be implemented using one or more computer systemswhich may be, for example, a general-purpose computer such as thosebased on an Intel PENTIUM®-type processor, a Motorola PowerPC®processor, a Hewlett-Packard PA-RISC® processor, a Sun UltraSPARC®processor, or any other type of processor or combination thereof.Alternatively, the computer system may include specially-programmed,special-purpose hardware, for example, an application-specificintegrated circuit (ASIC) or controllers intended for water treatmentsystems.

The computer system can include one or more processors typicallyconnected to one or more memory devices, which can comprise, forexample, any one or more of a disk drive memory, a flash memory device,a RAM memory device, or other device for storing data. The memory may beused for storing programs and data during operation of the system. Forexample, the memory may be used for storing historical data relating tothe parameters over a period of time, as well as operating data.Software, including programming code that implements embodiments of theinvention, can be stored on a computer readable and/or writeablenonvolatile recording medium, and then copied into memory wherein it canthen be executed by one or more processors. Such programming code may bewritten in any of a plurality of programming languages, for example,Java, Visual Basic, C, C#, or C++, Fortran, Pascal, Eiffel, Basic, orany of a variety of combinations thereof.

Components of the computer system may be coupled by one or moreinterconnection mechanisms, which may include one or more busses, e.g.,between components that are integrated within a same device, and/or anetwork, e.g., between components that reside on separate discretedevices. The interconnection mechanism may enable communications, e.g.,data and/or instructions, to be exchanged between components of thesystem.

The computer system can also include one or more input devices, forexample, a keyboard, mouse, trackball, microphone, touch screen, andother man-machine interface devices as well as one or more outputdevices, for example, a printing device, display screen, or speaker. Inaddition, the computer system may contain one or more interfaces thatcan connect the computer system to a communication network, in additionor as an alternative to the network that may be formed by one or more ofthe components of the system.

According to one or more embodiments of the invention, the one or moreinput devices may include sensors for measuring any one or moreparameters of any of the systems disclosed herein and/or componentsthereof. Alternatively, the sensors, the metering valves and/or pumps,or all of these components may be connected to a communication networkthat is operatively coupled to the computer system. Any one or more ofthe above may be coupled to another computer system or component tocommunicate with the computer system over one or more communicationnetworks. Such a configuration permits any sensor or signal-generatingdevice to be located at a significant distance from the computer systemand/or allow any sensor to be located at a significant distance from anysubsystem and/or the controller, while still providing datatherebetween. Such communication mechanisms may be affected by utilizingany suitable technique including but not limited to those utilizingwireless protocols.

The controller can include one or more computer storage media such asreadable and/or writeable nonvolatile recording medium in which signalscan be stored that define a program to be executed by one or moreprocessors. The medium may, for example, be a disk or flash memory. Intypical operation, the one or more processors can cause data, such ascode that implements one or more embodiments of the invention, to beread from the storage medium into a memory that allows for faster accessto the information by the one or more processors than does medium.

Although the computer system is described by way of example as one typeof computer system upon which various aspects of the invention may bepracticed, it should be appreciated that the invention is not limited tobeing implemented in software, or on the computer system as exemplarilyshown. Indeed, rather than implemented on, for example, a generalpurpose computer system, the controller, or components or subsectionsthereof, may alternatively be implemented as a dedicated system or as adedicated programmable logic controller (PLC) or in a distributedcontrol system. Further, it should be appreciated that one or morefeatures or aspects of the invention may be implemented in software,hardware or firmware, or any combination thereof. For example, one ormore segments of an algorithm executable by the controller 534 can beperformed in separate computers, which can be in communication with oneanother through one or more networks.

In some particular embodiments, the controller can be configured togenerate a plurality of output signals that initiates or terminates oneor more cycles or stages of the sequencing batch reactor. For example,the controller can generate an output signal that actuates one or moreinlet valves that fluidly connects one or more basins of the at leastone sequencing batch reactor to the source of water to be treated. Thecontroller can then generate a second output signal that preferably, butnot necessarily, closes the valve and, activates an aeration system ofat least one sequencing batch reactor to provide an oxygen source toachieve or maintain a target dissolved oxygen level of, for example,between about 0.5 and about 2 mg/L. The controller can thus beconfigured to facilitate biological sorption phenomena that aggregatesat least a portion of dissolved and suspended solids. The controller canthen generate a third output signal that promotes quiescent conditionsin at least one of the basins that provide settling of at least aportion of the settleable components. In some cases, quiescentconditions can be effected by terminating output signals and the thirdoutput signal can be generated by the controller to promote withdrawalof any of the supernatant, e.g., by decanting, or solids-rich portionsin the basin, after settling. Another output signal can then begenerated, e.g., a fifth output signal, that reactivates the aerationsystem. The controller can further generate a sixth output signal thatactivates, and a seventh output signal that deactivates an aerationsystem of at least one aerobic treatment tank to provide an oxygensource to achieve or maintain a target dissolved oxygen level of, forexample, between about 0.5 and about 2 mg/L.

Many municipal wastewater treatment plants experience diurnal influentvariation such as the example shown in FIG. 20. In some embodiments, abiosorption operation of a wastewater treatment system may become lessstable, for example, capturing more or less COD in influent wastewater,as loading conditions become more dynamic. If bio-sorption fails tocapture a sufficient amount of the COD, this may overload the capacityof a downstream anaerobic digester to efficiently process the COD. Tofacilitate enhancing the reliability of the performance of thebio-sorption process a control system that uses on-line instruments tocontrol the bio-sorption may be utilized.

A first level of control may include controlling a ratio of wastewaterflow to bio-sorption media in the bio-sorption operation. The sludgeinventory in the anaerobic digester is some systems may be greater thanthe sludge inventory in one or more other unit operations, so matchingthe anaerobic sludge recycle flow rate with the wastewater flow rate maynot present a great difficulty. Anaerobic sludge, however, is preferablyconditioned an aerobic environment with the help of some aerobic sludgeto become a re-useable bio-sorption media recycled to the bio-sorptionoperation. The inventory of aerobic sludge is often limited because bothcontact tank and stabilization tank are typically smaller than theanaerobic digester. As such, one control mechanism to facilitatestability of the operation of the treatment system may includedecreasing the amount of aerobic sludge flowed from the aerobicstabilization tank 818 to the bio-sorption tank 812 prior to receivingan increased inflow of wastewater to be treated, and increasing mixedliquor suspended solids (MLSS) in the aerobic stabilization tank 818 toincrease the aerobic sludge inventory. During periods of an increasedinfluent flow of wastewater to be treated, a stand-by aerobicstabilization tank may be utilized to increase the aerobic sludgeinventory. To maintain the duty and stand-by aerobic sludgestabilization tank both in good working condition (for example, tomaintain a sufficient population of live aerobic bacteria to aerobicallytreat MLSS or sludge introduced into the tanks at a desired rate), theymay be switched a few times a day. At peak COD loading conditions, bothaerobic stabilization tanks could be utilized.

Feed back control may be utilized in some embodiments of the controlsystem. An online COD or total organic carbon (TOC) meter may beutilized to measure the COD or TOC of solids-lean effluent leaving thefirst clarifier 814. When the effluent COD or TOC is at or above athreshold level at which the treatment system would efficiently treatthe influent wastewater, the ratio of an amount of aerobically treatedsolids-rich sludge output from the clarifier 814 to an amount ofanaerobically treated sludge output from the anaerobic digester (an“aerobic/anaerobic sludge ratio”) directed into the stabilization tank818 may be increased. This may be facilitated by for example, utilizinga controller, such as controller 534 of FIG. 3, to actuate one or morevalves to adjust the relative amounts of the solids-rich output of theclarifier 814 directed to the anaerobic digester 822 and to thestabilization tank 818 to a desired ratio. Additionally oralternatively, use of aerobic sludge stored in the stand-by aerobicstabilization tank may be initiated to introduce aerobically treatedsludge into the treatment system, for example into the stabilizationtank 818 or the sequencing batch reactor 812. When effluent COD or TOCis at a level such that the treatment system could efficiently treatwastewater having a higher COD or TOC level, the aerobic/anaerobicsludge ratio may be decreased and the duty and stand by aerobicstabilization tanks may be switched.

Without being bound to a particular theory, it is believed that bacteriaspecies might not be as important as floc morphology with respect to theeffectiveness of a bio-sorption media in adsorbing and absorbing MLSS.The floc morphology of anaerobically digested sludge can be modified orrepaired in an aerobic environment with the help of aerobic bacteria tomake anaerobic sludge a more effective bio-sorption media. The repairingkinetics may have good correlation with aerobic activity of theaerobic/anaerobic sludge mixture. Aerobic activity can be measured asspecific oxidation utilization rate (SOUR) or accumulation of SOUR. Forcontinuously stirred tank reactors reactors, accumulation of SOUR iscalculated as SOUR*Contact_time. SOUR may me measured by using adissolved oxygen probe to measure a change in dissolved oxygen in a tankof interest over time.

On some systems, the bio-sorption characteristic of sludge media and theSOUR in the contact tank and stabilization tank may be correlated. Forexample, when anaerobically digested sludge is recycled back to thestabilization tank, there are two sludge streams entering the aerobicstabilization tank: solids-rich sludge from the clarifier 814 andanaerobically digested sludge from the anaerobic digester. If the COD ofthe solids-lean effluent from the clarifier 814 is low, for example lessthan about 100 mg/L, in accordance with the above described system, thesoluble COD carried in the solids-rich sludge output from the clarifier814 would also be low, for example less than about 100 mg/L. A stableanaerobically digested sludge COD should also give a low (less thanabout 100 mg/L) COD in a recycled sludge produced in the contactstabilization tank 818. In some systems, the anaerobic sludge recyclestream has a very low flow rate, typically less than 1% of the averagedaily flow input to the treatment system. Therefore, soluble COD ofanaerobically digested sludge entering the stabilization tank should below (less than about 100 mg/L). As such, the SOUR in the stabilizationtank could become an indication of the aerobic activity of theaerobic/anaerobic sludge mixture that is not affected by a consistentlylow soluble COD present in the solids-rich output of the clarifier 814.If a sudden drop, for example a drop of about 30% or more within one ortwo hours, of SOUR in the stabilization tank is observed without asignificant change of the aerobic/anaerobically digested sludge ratio,it may indicate an unhealthy aerobic activity or inefficientanaerobically digested sludge repairing, which may lead to poorbio-sorption of COD in the contact tank. Upon this occurrence, theaerobic sludge stabilization tank may be put into a repairing stand-bystage and the stand-by aerobic sludge stabilization tank may utilized toprovide additional aerobic sludge.

Further aspects of the invention can involve or be directed tocomputer-readable media, or providing computer-readable media, thatfacilitates the various features of the treatment approaches describedherein.

For example, the computer-readable media can comprise instructionsimplementable on a computer system or a controller that performs amethod of treating wastewater in a wastewater treatment system, themethod comprising one or more steps of providing a wastewater to betreated, promoting biological sorption of the wastewater to be treatedto produce a first mixed liquor, producing a solids-rich sludge and asolids-lean portion from the mixed liquor, aerobically treating a firstportion of the solids-rich sludge to produce an at least partiallyaerobically treated sludge, anaerobically digesting a second portion ofthe solids-rich sludge to produce an anaerobically digested sludge,combining at least a portion of the at least partially aerobicallytreated sludge with the wastewater to be treated, and combining at leasta portion of the anaerobically digested sludge with the wastewater to betreated. The method can further comprise thickening the solids-richsludge to produce a thickened sludge and a sludge-lean portion andcombining at least a portion of the sludge-lean portion with thewastewater to be treated, wherein anaerobically digesting the secondportion of the solids-rich sludge comprises anaerobically digesting thethickened sludge to produce at least a portion of the anaerobicallydigested sludge. The method can further comprise aerobically treating atleast a portion of the solids-lean portion to produce a treated productand a second mixed liquor. The method can further comprise combining atleast a portion of the second mixed liquor with the wastewater to betreated. The method can further comprise aerobically treating at least aportion of the anaerobically digested sludge with the first portion ofthe solids-rich sludge to produce the at least partially aerobicallytreated sludge. The method can further comprise producing a solids-richwastewater and a solids-lean wastewater from the wastewater to betreated, and wherein promoting biological sorption of at least a portionof the wastewater to be treated comprises promoting biological sorptionof the solids-lean wastewater to produce the first mixed liquor. Themethod can further comprise introducing the solids-lean portion into amembrane bioreactor. The method can further comprise separating thewastewater to be treated into a solids-lean wastewater and a solids-richwastewater, promoting biological sorption of the solids-lean wastewaterto produce at least a portion of the first mixed liquor; andanaerobically digesting the solids-rich wastewater with the secondportion of the solids-rich sludge to produce the anaerobically digestedsludge and an off-gas comprising methane.

In other configurations, the computer-readable media can compriseinstructions implementable on a computer system or a controller thatperforms a method of treating wastewater in a wastewater treatmentsystem, the method having one or more steps for treating wastewatercomprising providing a wastewater stream to be treated, introducing thewastewater stream into a biological sorption tank to produce a firstmixed liquor stream, introducing the mixed liquor stream into aseparator to produce a solids-rich stream and a solids-lean stream,introducing at least a portion of the solids-rich stream into an aerobictreating tank to produce an at least partially aerobically treatedsludge stream, introducing at least a portion of the solids-rich streaminto an anaerobic digester to produce an anaerobically digested sludgestream, introducing at least a portion of the at least partiallyaerobically treated sludge stream into the biological sorption tank, andintroducing at least a portion of the anaerobically digested sludgestream into the biological sorption tank. The method can furthercomprise, in some cases, introducing at least a portion of thesolids-rich stream into a sludge thickener to produce a thickened sludgestream and a sludge-lean stream. In some cases, introducing at least aportion of the solids-rich stream into an anaerobic digester comprisesintroducing the thickened sludge stream into the anaerobic digester toproduce the anaerobically digested sludge stream. In still furthercases, introducing the wastewater stream into the biological sorptiontank comprises introducing the wastewater stream to be treated into aprimary separator to produce a solids-rich wastewater stream and asolids-lean wastewater stream, and introducing the solids-leanwastewater stream into the biological sorption tank to produce the firstmixed liquor stream. The method can further comprise introducing thesolids-rich wastewater stream into the anaerobic digester to produce atleast a portion of the anaerobically digested sludge stream. The methodcan further comprise introducing at least a portion of the anaerobicallydigested sludge stream into the aerobic treating tank to produce atleast a portion of the at least partially aerobically treated sludgestream. The method can further comprise introducing the solids-leanstream from the separator into a membrane bioreactor. The method canfurther comprise introducing at least a portion of the solids-leanstream into an aerobic polishing system to produce a treated stream anda second mixed liquor stream, and introducing at least a portion of thesecond mixed liquor stream into the biological sorption tank. The methodcan further comprise collecting an off-gas from the anaerobic digester,the off-gas comprising methane.

In other configurations, the computer-readable media can compriseinstructions implementable on a computer system or a controller thatperforms a method of treating wastewater in a wastewater treatmentsystem, the method having one or more steps for treating wastewatercomprising providing wastewater comprising dissolved and suspendedsolids, promoting aggregation of at least a portion of the dissolved andsuspended solids to produce a first mixed liquor, separating the firstmixed liquor into a first solids-lean portion and a first solids-richsludge, anaerobically digesting a first portion of the first solids-richsludge to produce an anaerobically digested sludge, separating theanaerobically digested sludge into a second solids-lean portion and asecond solids-rich sludge, precipitating one of a phosphorous containingcompound and a nitrogen containing compound from the second solids-leanportion, and combining a portion of the second solids-rich sludge withthe wastewater. The method can further comprise aerobically treating asecond portion of the first solids-rich sludge to produce an at leastpartially aerobically treated sludge. The method can further comprisecombining at least a portion of the at least partially aerobicallytreated sludge with the wastewater. The method can further comprisethickening the first portion of the first solids-rich sludge prior toanaerobically digesting the first portion of the first solids-richsludge. Thickening the first portion of the first solids-rich sludge maycomprise producing a solids-rich sludge having a first concentration ofmethanogenic bacteria, and anaerobically digesting the first portion ofthe first solids-rich sludge may comprise producing an anaerobicallydigested sludge having a second concentration of methanogenic bacteria,the first concentration being a significant fraction of the secondconcentration. The first concentration may be at least about 10% of thesecond concentration. The first concentration may be at least about 25%of the second concentration. The first concentration may be at leastabout 50% of the second concentration. The method can further compriseaerobically treating the portion of the second solids-rich sludge priorto combining the portion of the second solids-rich sludge with thewastewater. The method can further comprise combining a second portionof the first solids-rich sludge with the portion of the secondsolids-rich sludge. The method can further comprise separating asolids-lean fluid from the first solids-rich sludge prior toanaerobically digesting the first portion of the first solids-richsludge. The method can further comprise combining at least a portion ofthe solids-lean fluid with the second portion of the first solids-richsludge, and the portion of the second solids-rich sludge. The method canfurther comprise aerobically treating the combination of the at least aportion of the solids-lean fluid, the second portion of the firstsolids-rich sludge, and the portion of the second solids-rich sludge toform an at least partially aerobically treated combination. The methodcan further comprise combining the at least partially aerobicallytreated combination with the wastewater. The method can further compriseanoxically treating the wastewater and the at least partiallyaerobically treated combination to produce an anoxically treatedwastewater, and wherein promoting aggregation comprises introducingmethanogenic bacteria from the anaerobically digested sludge into thefirst mixed liquor. Precipitating one of the phosphorous containingcompound and the nitrogen containing compound from the secondsolids-lean portion may comprise adjusting a pH of the secondsolids-lean portion. Precipitating one of the phosphorous containingcompound and the nitrogen containing compound from the secondsolids-lean portion may comprise contacting the solids-lean portion withan alkali earth metal salt. The alkali earth metal salt may comprisemagnesium. The alkali earth metal salt may comprise magnesium chloride.Precipitating one of the phosphorous containing compound and thenitrogen containing compound from the second solids-lean portion maycomprise precipitating struvite from the second solids-lean portion.

In other configurations, the computer-readable media can compriseinstructions implementable on a computer system or a controller thatperforms a method of increasing the capacity of a wastewater treatmentsystem having a biological treatment train with at least one biologicalreactor selected from the group consisting of an anaerobic reactor, ananoxic reactor, and an aerobic reactor, a solids-rich outlet of thebiological treatment train fluidly connected upstream of an inlet of ananaerobic digester, and a recycle line fluidly connecting an outlet ofthe anaerobic digester to an inlet of the biological treatment train.The method may comprise adjusting a fraction of a solids-rich sludgeproduced in the biological treatment train directed to the inlet of theanaerobic digester to a level at which a concentration of methanogenicbacteria present in the solids-rich sludge produced in the biologicaltreatment train is a substantial fraction of a concentration ofmethanogenic bacteria present in mixed liquor in the anaerobic digester.The method may further comprise reducing a hydraulic retention time ofone of the at least one biological reactor and the anaerobic digester.The method may further comprise producing a biological floc in the atleast one biological reactor having an aerobic outer layer and one of ananoxic and an anaerobic core. Producing the biological floc in the atleast one biological reactor may comprise increasing the organic loadingof the at least one biological reactor. Producing the biological floc inthe at least one biological may comprise reducing an amount of oxygensupplied to the at least one biological reactor. The method may furthercomprise increasing a rate of production of methane in the anaerobicdigester. The method may further comprise directing methanogenicbacteria from the outlet of the anaerobic bacteria, through an aerobictreatment operation, and to the inlet of the anaerobic reactor.

The function and advantage of these and other embodiments of the systemsand techniques disclosed herein will be more fully understood from theexample below. The following example is intended to illustrate thebenefits of the disclosed treatment approach, but do not exemplify thefull scope thereof.

Example 1

Energy gain and sludge yield were estimated by numerically simulatingthe treatment system shown in FIG. 9. As illustrated, the proposedtreatment system was considered to have a primary clarifier 711 fluidlyconnected to the influent or source of wastewater to be treated. Theprimary clarifier was considered to produce a solids-lean wastewaterstream and a solids-rich wastewater stream. The solids-lean wastewaterwas considered to be introduced into a biological sorption tank 712 toproduce a mixed liquor, and the solids-rich wastewater stream wasconsidered to be introduced into an anaerobic digester 722. The mixedliquor from biological sorption tank 712 was considered to be introducedinto a separator 714 to produce a solids-lean stream which was to befurther treated in a membrane bioreactor, and a sludge stream. A portionof the sludge was to be introduced into a sludge thickener 724 toproduce a thickened sludge and a solids-lean sludge. Another portion ofthe sludge was considered to be introduced into an aerobic treatmenttank 716 to produce an at least partially aerobically treated sludgewhich was recycled and treated in biological sorption tank 712, with thesolids lean wastewater. The thickened sludge was considered to beintroduced into an anaerobic digester 722 to produce biologicallydigested sludge, of which a portion was recycled to be at leastpartially aerobically treated in treatment tank 716, and another portionof the digested sludge was discharged as solids waste 730.

The treatment system was numerically simulated using BIOWIN simulationsoftware, EnviroSim Associates Ltd., Ontario, Canada. The simulationruns were performed such that 2 to 20 percent of the solids-rich sludge816 exiting the separator or clarifier 714 was directed to the thickener724 and ultimately the anaerobic digester 722.

Typical wastewater concentrations were used for the simulations; anddetailed raw wastewater stoichiometry is listed in Table 1.

TABLE 1 Raw Wastewater Concentration and Stoichiometry (withcorresponding parameters for the BIOWIN simulation software). Flow rate(m³/day) 10,000 Total COD (mg/L) 600 Total Kjeldahl Nitrogen (TKN)(mg/L) 50 TSS (mg/L) 280 Fbs—Readily biodegradable (including Acetate)0.1600 (gCOD/g of total COD) Fac—Acetate (gCOD/g of readilybiodegradable COD) 0.1500 Fxsp—Non-colloidal slowly biodegradable 0.7500(gCOD/g of slowly degradable COD) Fus—Unbiodegradable soluble (gCOD/g oftotal COD) 0.0500 Fup—Unbiodegradable particulate (gCOD/g of total COD)0.1300 Fna—Ammonia (gNH₃—N/gTKN) 0.6600 Fnox—Particulate organicnitrogen (gN/g Organic N) 0.5000 Fnus—Soluble unbiodegradable TKN(gN/gTKN) 0.0200 FupN—N:COD ratio for unbiodegradable part. 0.0350 COD(gN/gCOD) Fpo4—Phosphate (gPO₄—P/gTP) 0.5000 FupP—P:COD ratio forinfluent unbiodegradable part. 0.0110 COD (gP/gCOD) FZbh—Non-poly-Pheterotrophs (gCOD/g of total COD) 0.0001 FZbm—Anoxic methanol utilizers(gCOD/g of total COD) 0.0001 Fzaob—Ammonia oxidizers (gCOD/g of totalCOD) 0.0001 Fznob—Nitrite oxidizers (gCOD/g of total COD) 0.0001Fzamob—Anaerobic ammonia oxidizers 0.0001 (gCOD/g of total COD)FZbp—PAOs (gCOD/g of total COD) 0.0001 FZbpa—Propionic acetogens (gCOD/gof total COD) 0.0001 Fzbam—Acetoclastic methanogens (gCOD/g of totalCOD) 0.0001 FZbhm—H₂-utilizing methanogens (gCOD/g of total COD) 0.0001

The following operating parameters of the main unit processes wereassumed.

Primary clarifier  60% TSS removal Sludge thickener  80% TSS removalTotal Return Activated Sludge 100% of influent flow (RAS) flowBiological sorption tank  500 m³ with DO set point of 2 mg/L Aerobicstabilization tank  600 m³ with DO set point of 2 mg/L Anaerobicdigester: 2900 m³

The following assumptions were made for the energy balance calculations.

-   -   The energy content of CH₄ is 35846 kJ/m³ (at 0° C. and 1 atm)        (Tchobanoglous et al., Wastewater Engineering Treatment and        Reuse, Metcalf & Eddy 2004)    -   Aeration energy efficiency in the biological sorption tank and        aerobic treatment tank would be 1.52 kg O₂/KWh (Tchobanoglous et        al., Wastewater Engineering Treatment and Reuse, Metcalf & Eddy        2004)    -   Mixing energy for the anaerobic digester would be 0.008 KW/m³        when the TSS concentration in anaerobic digester is less than 40        gram/L (Tchobanoglous et al., Wastewater Engineering Treatment        and Reuse, Metcalf & Eddy 2004)    -   Downstream membrane filtration air scouring and filtration        energy would be 0.2 kwh/m³ of effluent, and the O₂ transfer from        the MBR air scoring would be enough for nitrification    -   The mixed liquor entering the anaerobic digester will be heated        from 20° C. to 35° C., without heat exchange to recover energy.

When 2% of the RAS enters the anaerobic digester 722, all the digestereffluent is to be wasted out of the system as waste activated sludge730, and no anaerobic sludge is to be recycled back to biologicalsorption tank 712. The minimum RAS entering anaerobic digester 722appears to be about 2%.

The predicted energy gain from methane production, aeration energyreduction, net energy gain, percentage of the COD removal by theanaerobic digester and sludge yield are shown in FIGS. 4 to 8.

When 20% of RAS enters anaerobic digester 722, the simulation softwaregenerated the following data:

-   -   influent into primary clarifier 711: 6,000 kg COD/day    -   settled materials of out primary clarifier 711: 2,273 kg COD/day    -   effluent 718 out of secondary clarifier 714 to MBR: 1022 kg        COD/day    -   solids-lean portion out of sludge thickener 724: 2,205 kg        COD/day    -   thickened portion into anaerobic digester 722: 8,119 kg COD/day    -   effluent out of anaerobic digester 722: 7,045 kg COD/day    -   effluent out of anaerobic digester 722 to waste activated sludge        (WAS) outlet 730: 1,110 kg COD/day

The sludge retention time in the anaerobic digester 722 would be about16.1 days and the TSS concentration in the anaerobic digester 722 wouldbe 40,763 mg/L.

The aerobic sludge retention time, or MLSS inventory in biologicalsorption tank 712 and aerobic treatment tank 716 relative to a 20% RASmass flow rate would be 0.7 days.

The total COD removal would be 3,868 kg COD/day (6,000−1,110−1,022).

COD removal through the anaerobic digester 722 would be 3,347 kg COD perday (2,273+8,119−7,045), or a predicted removal rate of 87%(3,347/3,868).

Aerobic COD removal would be 13% so the aeration energy consumption islow, but probably still enough to mix the tanks.

About 87% of the COD removal would occur when 20% of RAS enters theanaerobic digester. Thus, about 20%, or less, of the RAS can beintroduced into the anaerobic digester to provide significant CODremoval.

When more sludge goes through anaerobic digester 722, the aerobicactivity decreases (see FIG. 5). When about 20% RAS enters the anaerobicdigester 722, the oxygen utilization rate (OUR) in the biologicalsorption tank 712 and the aerobic treatment tank 716 would be 21 mgO₂/Lper hour and 22 mgO₂/L per hour, respectively. Although 80% of the RASgoes through the aerobic treatment tank, the COD reduction rate in thattank appears to be low. The COD mass flow diagram at the condition of20% of return activated sludge entering the anaerobic digester is shownin FIG. 9, with COD mass flow rate in kgCOD/day.

Further, potential benefits may be realized in terms of increasedmethane and reduced sludge production with between about 5% to about 8%RAS anaerobically digested, which can avoid capital expendituresassociated with large anaerobic digestion processes.

The results also show that existing wastewater treatment facilities canbe modified or retrofitted to incorporate one or more various aspects ofthe systems and techniques disclosed herein to treat water at a reducedenergy rate and reduced amount of sludge.

Example 2

A simulation was performed to calculate the amount of methanogenicbacteria that would survive during recycling from an output of ananaerobic digester and back to the inlet of the anaerobic digester inaccordance with an embodiment of the apparatus 70 as is illustrated inFIG. 10. The simulated apparatus included a 14 liter aerobic biosorptioncontact tank 812, a 100 liter clarifier 814, a 50 liter stabilizationtank 818, a 100 liter sludge thickener 824, a 650 liter anaerobicdigester 822, an outlet 820 for treated water, and an outlet 830 forwaste sludge.

The simulation assumed an influent chemical oxygen demand (COD) at theinlet 810 of 600 mg/L and 6% anaerobic recycling (i.e., valvingdownstream of the solids-rich outlet of the clarifier 814 was configuredsuch that 6% of the solids-rich stream exiting the clarifier 814 wasdirected to the thickener 824, with the remaining 94% directed to thestabilization tank.) The sludge inventory in the aerobic contact tank812 was 25,484 kg and in the stabilization tank 818 was 194,436 kg. Witha total suspended solids mass flow rate to the sludge thickener of146,195 kg/day, the solids retention time in the contact stabilizationprocess was 1.5 days. The simulation also shows that there was 441 kgCOD/day of acetoclastic methanogens and 283 kg COD/day ofhydrogenotrophic methanogens to be recycled back to the contactstabilization process from the anaerobic digester 822 to thestabilization tank 818 and aerobic biosorption contact tank 812.

If 236 kg COD/day acetoclastic methanogens and 155 kg COD/dayhydrogenotrophic methanogens are recycled back to the anaerobicdigester, about 55% of the methanogens could survive in the contactstabilization process with a solids retention time of 1.5 days. Thissimulation result is based on default parameters in BIOWIN simulationsoftware including an acetoclastic methanogen aerobic cell decay rate of0.6 day⁻¹ and a hydrogenotrophic methanogen aerobic cell decay rate of0.6 day⁻¹.

This simulation indicates that because of the anaerobic sludge recyclein this process, a significant portion of the slow growing acetoclasticmethanogens and hydrogenotrophic methanogens may be recycled through theshort solids retention time contact stabilization process and back tothe anaerobic digester. As a result, the anaerobic digestion process inthis system would be more stable relative to systems not including amethanogenic bacteria recycle.

Example 3

Two treatment systems configured as illustrated in FIG. 12 (the testsystems 90) and one treatment system configured as in FIG. 13 (thecontrol system 100) were assembled with the following vessel sizes:

TABLE 2 Description FIG. 12, FIG. 13 Indicators Volume (liters) AnoxicTank 1111, 1311 25 Contact Tank 1112, 1312 14 Clarifier 1114, 1314 100Stabilization Tank 1116, 1316 50 Sludge Thickener 1124, 1324 100Anaerobic Digester 1122, 1322 650

The systems also included wastewater inlets 1110, 1310, clarified liquidoutlets 1120, 1320, and waste sludge outlets 1130, 1330.

The systems were operated by introducing a wastewater into the inlets1110, 1310 of the systems and flowing solid-rich and solid-lean streamsthrough the various portions of the systems in accordance with thefollowing tables.

TABLE 3 Test Systems Flow Rate Description FIG. 12 Indicator (ml/min)Input to Anoxic Tank 1210 420 Anoxic tank to Contact Tank 1211 874Contact Tank to Clarifier 1212 874 Clarifier to clarified liquid outlet1214 416 Clarifier to Stabilization Tank 1218 420 Clarifier to SludgeThickener 1220 38 Sludge Thickener to Stabilization Tank 1222 23 SludgeThickener to Anaerobic Digester 1224 15 Anaerobic Digester toStabilization Tank 1226 11 Anaerobic Digester to Waste Sludge 1228 4Outlet Stabilization Tank to Anoxic Tank 1230 454

TABLE 4 Control System Flow Rate Description FIG. 13 Indicator (ml/min)Input to Anoxic Tank 1410 420 Anoxic tank to Contact Tank 1411 844Contact Tank to Clarifier 1412 844 Clarifier to clarified liquid outlet1414 405 Clarifier to Stabilization Tank 1418 420 Clarifier to SludgeThickener 1420 19 Sludge Thickener to Stabilization Tank 1422 4 SludgeThickener to Anaerobic Digester 1424 15 Anaerobic Digester to WasteSludge 1428 15 Outlet Stabilization Tank to Anoxic Tank 1430 424

The amount of acetoclastic methanogens and hydrogenotrophic methanogensin the anaerobic digestion effluents and the anaerobic digestion feedstreams with and without anaerobic sludge recycle was quantified usingqPCR (quantitative real time polymerase chain reaction, a laboratorytechnique which is used to amplify and simultaneously quantify atargeted DNA molecule. It enables both detection and quantification ofone or more specific sequences in a DNA sample.) During stable operationof both the test processes and control process, samples were taken fromthe biosorption tanks, clarifier underflow, stabilization tanks, andanaerobic digesters for community analysis. DNA in each of the sludgesamples was rapidly extracted by using a PowerSoil® DNA extraction kit,available from MO BIO Laboratories, Inc., Carlsbad, Calif. The quantityand quality of the extracted DNA was checked by measuring absorbance at260 and 280 nm using a NanoDrop™ ND-1000 spectrophotometer, availablefrom NanoDrop Products, Wilmington, Del. DNA samples were shipped to alaboratory at Arizona State University, where the concentrations ofacetoclastic methanogens, hydrogenotrophic methanogens and some generalbacteria were measured using qPCR. Based on the data obtained, the celldecay rate of acetoclastic methanogens and hydrogenotrophic methanogensin an aerobic environment was calculated.

The results of the DNA analysis are illustrated in the charts of FIGS.14-16. FIGS. 14-16 illustrate the concentration of non-methanogenicbacteria (Bacteria) and methanogenic archaea (Archaea) in the influentwastewater, anoxic tanks 1111, 1311 (AX), the contact tanks 1112, 1312(CT), clarifiers 1114, 1314 (CL), sludge thickeners 1124, 1324 (SL), andanaerobic digesters 1122, 1322 (AD), as well as concentrations ofvolatile suspended solids (VSS) and total suspended solids (TSS) inthese tanks and in the sludge thickener (SL) and effluent wastewater inthe control system (Train 2), the first test system (Train 1) and thesecond test system (Train 3)

These results indicate that in general, Bacteria numbers correlate toVSS and TSS. The concentrations of Archaea are one to two orders ofmagnitude lower than Bacteria, but Archaea was observed in all tanksfrom which samples were taken. It appears that methanogens aresurviving, although qPCR does not assay viability or activity.

FIG. 17 illustrates how Archaea and Bacteria concentrations correlate inthe various tanks of each of the test and control systems. In thischart, the units of the Y axes are concentration of gene copies/mL. TheY axis on the left of the chart is for the Archaea data, while the Yaxis on the right of the chart is for the Bacteria data.

In this chart data was obtained from the various streams indicated bythe abbreviations on the X-axis of the chart as follows:

Qin=Influent

Qax T1=Stream leaving anoxic tank of Train 1

Qax T2=Stream leaving anoxic tank of Train 2

Qax T3=Stream leaving anoxic tank of Train 3

CT 1 T1=Stream leaving contact tank of Train 1

CT 1 T2=Stream leaving contact tank of Train 2

Qcl-stab T1=Solids-rich stream directed from the clarifier to thestabilization tank of train 1

Qcl-stab T2=Solids-rich stream directed from the clarifier to thestabilization tank of train 2

Qcl-stab T3=Solids-rich stream directed from the clarifier to thestabilization tank of train 3

QAD T1=Stream leaving anaerobic digester of Train 1

QAD T2=Stream leaving anaerobic digester of Train 2

QAD T3=Stream leaving anaerobic digester of Train 3

Qstab T1=Stream leaving stabilization tank of Train 1

Qstab T2=Stream leaving stabilization tank of Train 2

Qstab T3=Stream leaving stabilization tank of Train 3

In general, Bacteria and Archaea have an inverse relationship within thetreatment processes. This makes sense in that the conditions conduciveto the best bacterial growth (plenty of oxygen and nitrate) are inimicalto methanogens.

The Train 1 (the first test system, configured as illustrated in FIG.12) anaerobic digester was observed to have a greater concentration ofmethanogens than the anaerobic digester of both Train 2 (the controlsystem, configured as illustrated in FIG. 13) and Train 3 (the secondtest system, configured as illustrated in FIG. 12). Perhaps this is asign that Train 1 was operating better, for example, having a greatersurvival rate of methanogenic bacteria in the aerobic portions of thetreatment system, than Train 3.

Within the liquid-treatment processes, the test systems generally havehigher Archaea concentrations than the control system. This pattern doesnot hold for Bacteria.

These results indicate that a recycle of the anaerobiacally digestedsludge from the anaerobic digester into the stabilization tank and backto the anoxic tank of the treatment systems results in a significantincrease in the amount of methanogenic bacteria that is recycled back tothe inlet of the anaerobic digester.

FIG. 18 illustrates the daily biogas production from the two testsystems and the control system over a ten month period. As can be seen,the biogas production of the two test systems exceeded that of thecontrol system. This is likely due to an increased quantity ofmethanogenic bacteria in the anaerobic digester of the test systems ascompared to the control system The two test systems had an average dailybiogas production of 37.1±19.3 liter/day and 37.9±17.4 liter/day whilethe control system had an average daily biogas production of 23.8±11.3liter/day. These results indicate that systems operating with ananaerobic sludge recycle in accordance with the present invention mayconsistently produce more energy (in the form of methane gas) thansimilar systems without an anaerobic sludge recycle.

Example 4

A system such as that illustrated in FIG. 12 was utilized to study thepotential for recycling nitrification bacteria through the treatmentsystem. During the testing, an anaerobic sludge recycle percentage of 6%of the solids rich stream exiting the clarifier 1114 was directed to thethickener 1124, with the remaining 94% directed to the stabilizationtank 1116. The hydraulic retention time in the anoxic tank 1111 was onehour. The tank volumes and flow rates were the same as those indicatedin Tables two and three above.

Including the anoxic tank 1111 to perform de-nitrification upstream ofthe contact tank 1112 helped to reduce aerobic energy consumption as theresult of the de-nitrification oxygen credit, for example about 2.7 mgO₂/mg NO₃—N, and also reduce the likelihood of de-nitrification sludgethat could have floated in the clarifier 1114.

The feed stream from the thickener 1124 to the anaerobic digestersupplied 530 kg COD/day of Ammonia Oxidation Bacteria (AOB) and 57 kgNitrite Oxidation bacteria (NOB) to the inlet of the anaerobic digester1124.

The amount of AOB and NOB in the anaerobic digester influent andeffluent stream was analyzed using qPCR technology with primers relevantto AOB and NOB.

The specific nitrate production rate of a sample of aerobically treatedsludge taken from the inlet of the anaerobic digester and of a sample ofanaerobically digested sludge taken from the outlet of the anaerobicdigester were measured to quantify the specific nitrification activityof the anaerobically digested sludge. At time zero, the NO₃—Nconcentrations of the sludge samples were measured and 10 mg/L NH₃—N wasadded to each sample to ensure sufficient NH₃ was present to continue toreact throughout the time period of the test. Both sludge samples werethen aerated to achieve and maintain a dissolved oxygen level of 2 mg/L.After two hours of aeration, the NO₃—N concentrations of the sludgesamples was measured again and the specific nitrification rate (SNR) ofeach was calculated as: SNR=(NO₃—N_(time=2hr)−NO₃—N_(time=0)) (MixedLiquor Volatile Suspended Solids).

The results of this test are illustrated in table 5 below.

TABLE 5 Nitrification Bacteria Recycle Test Results Sample from Samplefrom Original Original Anaerobic Anaerobic Param- Digester DigesterDigester Inlet Digester Outlet eter Inlet* Outlet* T0 T 2 hr T0 T 2 hrNO₂-N — — 0.013 1.668 0.009 0.482 (ppm) NO₃-N 0.07 0.115 0.049 4.6450.079 1.325 (ppm) NH₃-N 14.97 129.1 8.93 4.84 31.05 29.82 (ppm) pH 7.067.32 7.21 6.16 7.38 7.75 TSS 17.9 15.16 5.62 5.7 4.86 5.22 (mg/l) VSS10.2 8.1 2.72 2.76 2.26 2.16 (mg/l) *The “Original Digester Inlet” and“Original Digester Outlet” columns refer to measurements performed atthe anaerobic digester inlet and outlet, respectively, prior toinitiating a recycle of anaerobically digested sludge from the anaerobicdigester to the stabilization tank 1116.

From the data for the NO₃—N in the samples from the anaerobic digesterinlet and outlet, it was calculated that the nitrification activity ofthe sludge entering the anaerobic digester (the aerobically treatedsludge) was 4.645-0.049=4.596 mg/l in 2 hours. The nitrificationactivity of the sludge leaving the anaerobic digester (the anaerobicallydigested sludge) was 1.325-0.079=1.246 mg/l in 2 hours. Therefore1.246/4.596=27% of the nitrification activity survived and was availablefor recycling back from anaerobic digester to the inlet of thewastewater treatment system.

Accordingly, the recycling of anaerobically digested sludge to the inletand/or contact tank 1111 of the treatment system may provide NOB and AOBwhich may assist in the nitrification process in the aerobic portions ofthe treatment system, and potentially provide for a reduced volume ofaerobic treatment vessels and thus a reduced hydraulic residence time inthese vessels, or an increase in a safety factor which would render thenitrification process more resistant to failure due to disruptions inthe operation of the treatment system. It is expected that decreasingthe solids retention time in the anaerobic digester would furtherincrease the AOB and NOB survival percentage.

Example 5

A phosphorous and nitrogen recovery simulation was performed utilizingBIOWIN simulation software for a hypothetical activated sludge treatmentsystem configured as illustrated in FIG. 11. The simulation assumed anaverage daily wastewater input flow (ADF) of 350,000 m³/day, an influentCOD of 600 mg/L, a total influent phosphorous concentration (TP) of 10mg/L, an anaerobic recycle fraction (the volume fraction of thesolids-rich output from the clarifier 914 directed into the anaerobicreactor 922) of 6%, a hydraulic residence time in the anaerobictreatment tank 911 of one hour, and a hydraulic residence time in theaerobic treatment tank 912 of four hours.

The simulation assumed 3,500 m³/day of anaerobically digested sludge wasmixed with 3,500 m³/day of a solids-lean stream output from theclarifier 915 at an inlet of the separator 926. A solids-lean effluentflow from the separator 926 flow was set at 3,500 m³/day, 1% of the ADF.1,554 kg/day of phosphorus and 1,925 kg/day of nitrogen was calculatedto be present in the effluent from the separator 926. With a totalphosphorus load to the plant of 3,500 kg/day, about 44% of the totalphosphorous in the wastewater could be recovered, 10% carried out in theeffluent and 46% still contained in the WAS. Because of the phosphorusrecovery, the total phosphorous (TP) present in the effluent to output920 also decreased from 1.7 mg/L to 1.08 mg/L.

The amount of nitrogen that could be removed from the effluent flow fromthe separator 926 was calculated to be 1,925 kg/day, which is 8% of thetotal nitrogen in the influent wastewater (22,750 kg N/day). As theresult of precipitation in a precipitation vessel 940 (for example, byprecipitating struvite from the effluent flow from the separator 926 byintroduction of, for example, magnesium chloride into the effluent), 702kg N/day could be removed. The remaining nitrogen in the streamintroduced into the precipitation vessel after precipitation of thenitrogen would be about 1,223 kg/day or 5% of the total nitrogen load.Further treatment, for example utilizing an anaerobic ammonium oxidationprocess could remove additional nitrogen from the stream introduced intothe precipitation vessel after precipitation of the nitrogen.

Example 7

A simulation was performed using BIOWIN simulation software to determinepotential energy generation rates for a system such as illustrated inFIG. 10 under different conditions of influent wastewater COD levels anddifferent percentages of solids-rich sludge generated in the clarifier814 directed to the sludge thickener 824 and anaerobic digester 822. Thecharacteristics of hypothetical representative wastewater with threedifferent COD levels used in the simulation were set as follows:

TABLE 6 Influent characteristics for the process simulations Low CODMedium COD High COD COD (mg/l) 300 600 800 TSS (mg/l) 150 258 330 VSS(mg/l) 117 234 312 TKN (mg/l) 38 65 83 NH₃—N (mg/l) 25 43 55 TP (mg/l)10 10 10 Temperature 20 20 20 (degrees C.)

Because the COD/TSS ratio given are not a constant, the VSS/TSS ratiowas set at different values so that the BIOWIN simulation softwaredefault typical influent COD, TN, and TP factions could be used. TheCOD, TN, and TP fractions are listed in Table 7 below.

TABLE 7 COD, TN and TP fraction used for the process simulations Readilybiodegradable (including Acetate) (gCOD/g of total 0.1600 COD) Acetate(gCOD/g of readily biodegradable COD) 0.1500 Non-colloidal slowlybiodegradable (gCOD/g of slowly 0.7500 degradable COD) Unbiodegradablesoluble (gCOD/g of total COD) 0.0500 Unbiodegradable particulate (gCOD/gof total COD 0.1300 Ammonia (gNH₃—N/gTKN) 0.6600 Particulate organicnitrogen (gN/g Organic N) 0.5000 Soluble unbiodegradable TKN (gN/gTKN)0.0200 N:COD ratio for unbiodegradable part. COD (gN/gCOD) 0.0350Phosphate (gPO₄—P/gTP) 0.5000 P:COD ratio for unbiodegradable part. COD(gP/gCOD) 0.0110 Non-poly-P heterotrophs (gCOD/g of total COD) 0.0001Anoxic methanol utilizers (gCOD/g of total COD) 0.0001 Ammonia oxidizers(gCOD/g of total COD) 0.0001 Nitrite oxidizers (gCOD/g of total COD)0.0001 Anaerobic ammonia oxidizers (gCOD/g of total COD) 0.0001 PAOs(gCOD/g of total COD) 0.0001 Propionic acetogens (gCOD/g of total COD)0.0001 Acetoclastic methanogens (gCOD/g of total COD) 0.0001H₂-utilizing methanogens (gCOD/g of total COD) 0.0001

The DO of the contact tank 812 and the stabilization tank 818 were setat 2 mg/l. The HRT in the stabilization tank 818 was set at 2 hours. TheHRT/SRT in the anaerobic digester was set at 30 days at a temperature of35° C. The HRT in the contact tank 812 was set at 0.5 hours for theinfluent COD=300 mg/l and 600 mg/l scenarios. For the influent COD=800mg/l scenarios, the HRT in the contact tank 812 was increased to onehour.

The energy consumption of the simulated system was calculated based onthe following assumptions: The energy content of methane is 35,846 kJ/m³(at 0° C. and 1 atm.) 35% of the energy in the methane will be convertedto electricity and 65% converted to heat. The heat will be used to heatthe sludge from 20° C. to 35° C. The surplus heat energy will not beconsidered in the flowing electric energy calculations. Actual OxygenRequirement (AOR) of in the contact tank and stabilization tank wascalculated based on OUR, HRT and ADF. Because the effluent NH₃—N ishigher than 5 mg/l, further nitrification AOR is calculated based on4.57 gram of oxygen per gram of NH₃—N to be nitrified. Aeration electricenergy efficiency in the contact tank 812 and aerobic stabilization tank818 is 1.52 kg. oxygen/kwh. Total pumping energy was estimated based onan ADF of 350,000 m³/day, Total Dynamic Head (TDH)=2. Meter and pump andmotor total efficiency was assumed to be 50%. Mixing electric energy foranaerobic digester was assumed to be 0.008 kw/m³ when the TSSconcentration in AD is less than 40 gram/liter.

The process was simulated at multiple influent COD concentrations atdifferent AN sludge recycle percentage up to 12%. The main results ofelectric and heat energy gain from methane, total and specificelectricity consumption, fractions of AE and AN COD biodegradation,sludge yield and effluent water quality are shown in Tables 8-10 below.

TABLE 8 Calculation results for influent COD = 300 mg/l scenariosAnaerobic sludge recycle percentage n/a   4%    6%   10%   12% Influentwastewater flow rate (m³/day) 350,000 350,000 350,000 350,000 350,000COD (mg/l) 300 300 300 300 300 TKN (mg/l) 38 38 38 38 38 TSS (mg/l) 150150 150 150 150 CH₄ produced (m³/day) @ 0° C. 1 atm.)* 6,813 10,24112,380 16,996 18,408 Energy in CH₄ (kwh/day) 67,839 101,976 123,266169,234 183,291 Electricity from CH₄ (kwh/day) 23,744 35,691 43,14359,232 64,152 Heat from CH₄ (kwh/day) 44,095 66,284 80,123 110,002119,139 Sludge temp. (° C.) 20 20 20 20 20 Anaerobic digester temp (°C.) 35 35 35 35 35 Heat required (kwh/day) 61,058 61,058 61,058 61,05861,058 Is heat enough? no yes yes yes yes OUR in contact tank (g/m³/hr)*83 63 47 21 14 HRT in contact tank (hr) 0.5 0.5 0.5 0.5 0.5 AOR incontact tank (kg/day) 14,506 10,978 8,285 3,714 2,405 OUR instabilization tank (g/m³/hr)* 79 65 51 22 14 HRT in stabilization tank(hr) 2 2 2 2 2 AOR in stabilization tank (kg/day) 55,307 45,689 35,42015,078 9,961 Effluent NH₃—N (mg/l)* 11.5 15.7 21.8 29.2 29.6 Furthernitrification AOR (kg.O_(2/)day) 10,317 17,051 26,904 38,644 39,300Total AOR (kg.O_(2/)day) 80,130 73,717 70,608 57,435 51,665 Energyconsumption for O₂ transfer (kwh/day) 52,717 48,498 46,453 37,786 33,990Volume of AD (m³) 105,000 105,000 105,000 105,000 105,000 Mixing energyfor Anaerobic Digester (kwh/day) 20,160 20,160 20,160 20,160 20,160Estimated TDH (m) 2.00 2.00 2.00 2.00 2.00 Total pumping energy(kwh/day) 3,811 3,811 3,811 3,811 3,811 Total electricity consumption(kwh/day) 76,688 72,469 70,424 61,758 57,961 Electricity usage w/o CH₄generated electricity 52,944 36,778 27,281 2,526 −6,191 (kwh/day)Specific energy consumption (khw/m³) 0.15 0.11 0.08 0.01 −0.02 EffluentCOD (kg/day)* 12,175 13,368 14,800 20,646 23,751 Percentage of total CODload 11.60% 12.73% 14.10% 19.66% 22.62% WAS COD (kg.COD/day)* 25,08120,831 18,862 16,348 15,416 Percentage of total COD load 23.89% 19.84%17.96% 15.57% 14.68% Anaerobic digester COD removal (kg.COD/day)* 20,14430,055 36,228 49,606 53,703 Percentage of total COD load 19.19% 28.62%34.50% 47.24% 51.15% Aerobic tank COD removal (kg.COD/day)* 47,60040,747 35,110 18,400 12,130 Percentage of total COD load 45.33% 38.81%33.44% 17.52% 11.55% VSS in WAS (kg/day)* 16,166 13,513 12,223 10,4779,830 Sludge yield (VSS/COD) 0.15 0.13 0.12 0.10 0.09 Sludge yield(VSS/BOD) 0.08 0.06 0.06 0.05 0.05 *Data obtained from processsimulation

TABLE 9 Calculation results for influent COD = 600 mg/l scenariosAnaerobic sludge recycle percentage n/a   4%    6%   10%   12% Influentwastewater flow rate (m³/day) 350,000 350,000 350,000 350,000 350,000COD (mg/l) 600 600 600 600 600 TKN (mg/l) 65 65 65 65 65 TSS (mg/l) 258258 258 258 258 CH₄ produced (m³/day) @ 0° C. 1 atm.)* 19,593 20,20724,816 34,627 37,886 Energy in CH₄ (kwh/day) 195,088 201,210 247,096344,785 377,236 Electricity from CH₄ (kwh/day) 68,281 70,424 86,484120,675 132,033 Heat from CH₄ (kwh/day) 126,807 130,787 160,612 224,110245,203 Sludge temp. (° C.) 20 20 20 20 20 Anaerobic digester temp (°C.) 35 35 35 35 35 Heat required (kwh/day) 61,058 61,058 61,058 61,05861,058 Is heat enough? Yes Yes Yes Yes Yes OUR in contact tank(g/m³/hr)* 120 100 100 49 33 HRT in contact tank (hr) 0.5 0.5 0.5 0.50.5 AOR in contact tank (kg/day) 20,988 17,434 17,434 8,645 5,815 OUR instabilization tank (g/m³/hr)* 113 95 95 44 30 HRT in stabilization tank(hr) 2 2 2 2 2 AOR in stabilization tank (kg/day) 78,771 66,535 66,53530,996 20,930 Effluent NH₃—N (mg/l)* 24.6 25.4 35.3 47.9 49.7 Furthernitrification AOR (kg.O_(2/)day) 31,366 32,582 48,417 68,667 71,418Total AOR (kg.O_(2/)day) 131,125 116,550 132,385 108,308 98,163 Energyconsumption for O₂ transfer (kwh/day) 86,266 76,678 87,096 71,255 64,581Volume of AD (m³) 105,000 105,000 105,000 105,000 105,000 Mixing energyfor Anaerobic Digester (kwh/day) 20,160 20,160 20,160 20,160 20,160Estimated TDH (m) 2 2 2 2 2 Total pumping energy (kwh/day) 3,811 3,8113,811 3,811 3,811 Total electricity consumption (kwh/day) 110,238100,649 111,067 95,226 88,552 Electricity usage w/o CH₄ generatedelectricity 41,957 30,225 24,583 −25,449 −43,481 (kwh/day) Specificenergy consumption (khw/m³) 0.12 0.09 0.07 −0.07 −0.12 Effluent COD(kg/day)* 20,296 21,109 23,005 33,592 41,020 Percentage of total CODload  9.66% 10.05% 10.95% 16.00% 19.53% WAS COD (kg.COD/day)* 52,86448,613 43,708 36,652 32,372 Percentage of total COD load 25.17% 23.15%20.81% 17.45% 15.42% Anaerobic digester COD removal (kg.COD/day)* 57,25459,064 72,403 100,865 110,330 Percentage of total COD load 27.26% 28.13%34.48% 48.03% 52.54% Aerobic tank COD removal (kg.COD/day)* 79,58581,214 70,884 38,891 26,278 Percentage of total COD load 37.90% 38.67%33.75% 18.52% 12.51% VSS in WAS (kg/day)* 34,225 31,549 28,340 23,52320,682 Sludge yield (VSS/COD) 0.16 0.15 0.13 0.11 0.10 Sludge yield(VSS/BOD) 0.08 0.08 0.07 0.06 0.05 * Data obtained from processsimulation

TABLE 10 Calculation results for influent COD = 800 mg/l scenariosAnaerobic sludge recycle percentage n/a    6%   10%   12% Influentwastewater flow rate (m³/day) 350,000 350,000 350,000 350,000 COD (mg/l)800 800 800 800 TKN (mg/l) 83 83 83 83 TSS (mg/l) 330 330 330 330 CH₄produced (m³/day) @ 0° C. 1 atm.)* 26,631 31,656 43,260 49,093 Energy inCH₄ (kwh/day) 265,170 315,201 430,753 488,827 Electricity from CH₄(kwh/day) 92,809 110,320 150,764 171,089 Heat from CH₄ (kwh/day) 172,360204,881 279,990 317,737 Sludge temp. (° C.) 20 20 20 20 Anaerobicdigester temp (° C.) 35 35 35 35 Heat required (kwh/day) 61,058 61,05861,058 61,058 Is heat enough? yes yes yes yes OUR in contact tank(g/m³/hr)* 112 105 69 50 HRT in contact tank (hr) 1 1 1 1 AOR in contacttank (kg/day) 39,057 36,873 24,077 17,406 OUR in stabilization tank(g/m³/hr)* 120 118 68 46 HRT in stabilization tank (hr) 2 2 2 2 AOR instabilization tank (kg/day) 84,308 82,488 47,453 32,368 Effluent NH₃—N(mg/l)* 39.9 41.5 58.9 60.5 Further nitrification AOR (kg.O_(2/)day)55,887 58,446 86,149 88,740 Total AOR (kg.O_(2/)day) 179,251 119,36171,530 49,774 Energy consumption for O₂ transfer (kwh/day) 117,92878,527 47,059 32,746 Volume of AD (m³) 105,000 105,000 105,000 105,000Mixing energy for Anaerobic Digester (kwh/day) 20,160 20,160 20,16020,160 Estimated TDH (m) 2 2 2 2 Total pumping energy (kwh/day) 3,8113,811 3,811 3,811 Total electricity consumption (kwh/day) 141,899102,498 71,030 56,717 Electricity usage w/o CH₄ generated electricity49,090 −7,823 −79,734 −114,373 (kwh/day) Specific energy consumption(khw/m³) 0.14 −0.02 −0.23 −0.33 Effluent COD (kg/day)* 23,120 24,17128,398 34,760 Percentage of total COD load  8.26%  8.63% 10.14% 12.41%WAS COD (kg.COD/day)* 71,057 62,991 55,294 53,118 Percentage of totalCOD load 25.38% 22.50% 19.75% 18.97% Anaerobic digester COD removal(kg.COD/day)* 77,691 92,317 125,958 142,920 Percentage of total COD load27.75% 32.97% 44.99% 51.04% Aerobic tank COD removal (kg.COD/day)*108,132 100,521 70,350 49,202 Percentage of total COD load 38.62% 35.90%25.12% 17.57% VSS in WAS (kg/day)* 46,098 40,903 35,676 34,068 Sludgeyield (VSS/COD) 0.16 0.15 0.13 0.12 Sludge yield (VSS/BOD) 0.08 0.070.06 0.06 *Data obtained from process simulation

FIG. 20 illustrates anaerobic COD removal at the various anaerobicsludge recycle percentages at the different wastewater COD loadings. Asis shown in FIG. 21, more and more COD was biodegraded in the anaerobicdigester when the anaerobic sludge recycle percentage increased. As theresult, the methane production also increased with increasing anaerobicsludge recycle percentage. Take the influent COD=600 mg/l scenarios asan example. For example, in the COD=600 mg/l scenario, methaneproduction increased from 19,593 m³/day to 18,408 m³/day. Theelectricity and heat recovery from methane increased from 68,281 kWh/dayto 132,033 kWh/day and from 126,807 kWh/day to 245,203 kWh/day,respectively. For the majority of the simulated scenarios, the heatrecovery from the methane was more than enough to heat the sludge from20° C. to 35° C.

FIG. 21 illustrates aerobic COD removal at the various anaerobic sludgerecycle percentages at the different wastewater COD loadings. As isshown in FIG. 22, less COD was aerobically removed when the anaerobicsludge recycle percentage increased. When increasing amounts ofanaerobic sludge recycles into the activated sludge system, it graduallychanged the ecology of activated sludge system, making aerobic bacterialess dominant and the sludge more like an inert bio-sorption media. Forexample, in the wastewater COD=600 mg/l scenario, the oxygen utilizationrate in the contact tank and in the stabilization tank decreased from120 mg/l/hr to 33 mg/l/hr and from 113 mg/l/hr to 30 mg/l/hr,respectively. Because of the OUR or the AE activity decrease, the AORdecreased from 13,125 kg. oxygen/day to 98,163 kg. oxygen/day and oxygentransfer electric energy consumption decreased from 86,266 kWh/day to64,581 kWh/day.

As illustrated in FIG. 22, because of more anaerobic COD biodegradationto recover energy and less aerobic COD biodegradation to consume energy,the specific energy consumption to treat the wastewater decreasedsignificantly with the anaerobic recycle ratio. For example, as shown inTable 10 above, as the anaerobic recycle ratio increased from 0 to 12%,the anaerobic energy recovery, measured as energy in CH₄ produced,increased from 265,170 kwh/day to 488,827 khw/day, while the energyconsumed in the aerobic biodegradation process, measured as energyconsumption for O₂ transfer, decreased from 117,928 kwh/day to 32,746kwh/day, resulting in a change in specific energy consumption of from0.14 kwh/m³ to −0.33 kwh/m³. These results indicate that specific energyconsumption of less than about 0.1 kwh/m³ is achievable by using theprocess disclosed in the present disclosure. With the anaerobic sludgerecycle set at about 6%, the process results in a specific energyconsumption very close to 0.1 kWh/m³ for wastewater with a COD ofbetween about 300 mg/L and about 600 mg/L. With a higher anaerobicsludge recycle percentage, such as about 12%, it is also possible toachieve zero energy consumption when the influent COD=300 mg/l and theenergy recovery potential may be net positive when influent COD=600 mg/lor 800 mg/l.

Further, as illustrated in FIG. 23, because more COD is biodegraded byfollowing the anaerobic bio-pathway which has a lower sludge yield thanan aerobic process, the system total sludge production was alsodecreased with increasing anaerobic sludge recycle percentage. Lesssludge production will decrease the sludge handling cost and alsopotentially offer opportunities for nutrient recovery.

Those skilled in the art would readily appreciate that the variousparameters and configurations described herein are meant to be exemplaryand that actual parameters and configurations will depend upon thespecific application for which the systems and methods of the presentinvention are used. Those skilled in the art will recognize, or be ableto ascertain using no more than routine experimentation, manyequivalents to the specific embodiments described herein. For example,those skilled in the art may recognize that the system, and componentsthereof, according to the present invention may further comprise anetwork of systems or be a component of treatment system. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, the disclosed treatment systems and techniquesmay be practiced otherwise than as specifically described. For example,although the term “supernatant” has been used herein to refer toseparation product, the term has been used only for illustrativepurposes and its use does not limit the scope of the claims to aparticular separation technique. The present treatment systems andtechniques are directed to each individual feature, system, or methoddescribed herein. In addition, any combination of two or more suchfeatures, systems or methods, if such features, systems or methods arenot mutually inconsistent, is included within the scope of the presentinvention.

Further, it is to be appreciated various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. For example, a portion of solids-rich stream or thesludge stream can be introduced to an upstream unit operation, such as aprimary clarifier, or a biological sorption tank, or both. In othercases, the solids-leans portion or the sludge-lean portion can bedirected to another separator and/or to a polishing unit. In otherinstances, an existing treatment facility may be modified to utilize orincorporate any one or more aspects of the invention. Thus, in somecases, the treatment systems can involve connecting or configuring anexisting facility to comprise an aerobic digester, optionally with abiological sorption tank, and an aerobic treatment tank. Accordingly,the foregoing description and drawings are by way of example only.Further, the depictions in the drawings do not limit the inventions tothe particularly illustrated representations. For example, one or morebiological reactors may be utilized in one or more trains of thetreatment system.

Use of ordinal terms such as “first,” “second,” “third,” and the like inthe specification and claims to modify an element does not by itselfconnote any priority, precedence, or order of one element over anotheror the temporal order in which acts of a method are performed, but areused merely as labels to distinguish one element having a certain namefrom another element having a same name, but for use of the ordinalterm, to distinguish the elements.

What is claimed is:
 1. A method for treating wastewater comprising:providing a wastewater to be treated; promoting biological sorption ofthe wastewater to be treated in a biological sorption contact tank toproduce a mixed liquor; producing a solids-rich sludge and a solids-leanportion from the mixed liquor; combining a first portion of thesolids-rich sludge with the wastewater to be treated; introducing asecond portion of the solids-rich sludge into a sludge thickener toproduce a thickened sludge and a sludge-lean stream; combining thesludge-lean stream with the wastewater to be treated; anaerobicallydigesting the thickened sludge to produce an anaerobically digestedsludge; combining a first portion of the anaerobically digested sludgewith the wastewater to be treated; aerobically treating a second portionof the anaerobically digested sludge to form an at least partiallyaerobically treated sludge; and combining the at least partiallyaerobically treated sludge with the wastewater to be treated.
 2. Themethod of claim 1, further comprising directing the first portion of thesolids-rich sludge into a stabilization tank prior to combining thefirst portion of the solids-rich sludge with the wastewater to betreated.
 3. The method of claim 2, further comprising directing agreater amount of the solids-rich sludge into the stabilization tankthan into the sludge thickener.
 4. The method of claim 2, furthercomprising directing the sludge-lean stream into the stabilization tankprior to combining the sludge-lean stream with the wastewater to betreated.
 5. The method of claim 4, further comprising directing thefirst portion of the anaerobically digested sludge into thestabilization tank prior to combining the first portion of theanaerobically digested sludge with the wastewater to be treated.
 6. Themethod of claim 5, further comprising directing the portion of the atleast partially aerobically treated sludge to the biological sorptioncontact tank.
 7. The method of claim 1, further comprising directing thesludge-lean stream into a stabilization tank prior to combining thesludge-lean stream with the wastewater to be treated.
 8. The method ofclaim 1, further comprising directing the first portion of theanaerobically digested sludge into a stabilization tank prior tocombining the first portion of the anaerobically digested sludge withthe wastewater to be treated.
 9. The method of claim 1, furthercomprising directing the portion of the at least partially aerobicallytreated sludge to the biological sorption contact tank.
 10. A method fortreating wastewater comprising: providing a wastewater to be treated;separating the wastewater to be treated into a solids-lean wastewaterand a solids-rich wastewater; promoting biological sorption of thesolids-lean wastewater in a biological sorption contact tank to producea mixed liquor; producing a solids-rich sludge and a solids-lean portionfrom the mixed liquor; combining a first portion of the solids-richsludge with the wastewater to be treated; introducing a second portionof the solids-rich sludge into a sludge thickener to produce a thickenedsludge and a sludge-lean stream; combining the sludge-lean stream withthe wastewater to be treated; directing the thickened sludge togetherwith the solids-rich wastewater into an anaerobic digester;anaerobically digesting the thickened sludge and the solids-richwastewater together in the anaerobic digester to produce ananaerobically digested sludge; and combining a first portion of theanaerobically digested sludge with the wastewater to be treated.